He was the son of Landgrave William II of Hesse and his second wife Anna of Mecklenburg - Schwerin. His father died when Philip was five years old, and in 1514 his mother, after a series of struggles with the estates of Hesse, succeeded in becoming regent for him. The controversies still continued, however, so that, to put an end to them, Philip was declared to have attained his majority in 1518, his actual assumption of power beginning in the following year. The power of the estates had been broken by his mother, but he owed her little else. His education had been very imperfect, and his moral and religious training had been neglected. Despite all this, he developed rapidly as a statesman, and soon began to take steps to increase his personal authority as a ruler.

The first meeting of Philip of Hesse with Luther was in 1521 at the Diet of Worms, where he was attracted by the Reformer's personality, though he had at first little interest in the religious elements of the situation. He embraced Protestantism in 1524 after a personal meeting with Philipp Melanchthon, helped suppress the German Peasants' War defeating Thomas Müntzer at Frankenhausen.

He refused to be drawn into the anti - Lutheran league of George, Duke of Saxony, in 1525; and by his alliance with John, Elector of Saxony, concluded at Gotha 27 February 1526, showed that he was already taking steps to organize a protective alliance of all Protestant princes and powers. At the same time he united political motives with his religious policy, aiming, as early as the spring of 1526, to prevent the election of Archduke Ferdinand as emperor of the Holy Roman Empire. At the Diet of Speyer Philip openly championed the Protestant cause, rendering it possible for Protestant preachers to propagate their views while the Diet was in session, and, like his followers, openly disregarding ordinary Roman Catholic ecclesiastical usages.

Although there was no strong popular movement for reforming Hesse, Philip determined to organize the church there according to Protestant principles. In this he was aided not only by his chancellor, the humanistic Feige of Lichtenau, and his chaplain, Adam Krafft, but also by the ex-Franciscan François Lambert d'Avignon, a fanatical enemy of the faith he had left. While the violent policy of Lambert, embodied, at least in part, in the Homberg church order was abandoned, and an essentially Lutheran type of organization was adopted, the monasteries and religious foundations were dissolved; their property was applied to charitable and scholastic purposes; and the University of Marburg was founded in the summer of 1527 to be, like Wittenberg, a school for Protestant theologians.

Philip's father - in - law and the bishops of Würzburg and Mainz were active in agitating against the growth of the Reformation, and the combination of several circumstances, including rumors of war, convinced Philip of the existence of a secret league among the Roman Catholic princes. His suspicions were confirmed to his own satisfaction by a forgery given him by an adventurer who had been employed in important missions by George of Saxony, one Otto von Pack; and after meeting with the Elector John of Saxony at Weimar on 9 March 1528, it was agreed that the Protestant princes should take the offensive in order to protect their territory from invasion and capture.

Both Luther and the elector's chancellor, Brück, though convinced of the existence of the conspiracy, counseled strongly against acting on the offensive. The imperial authorities at Speyer now forbade all breach of the peace, and, after long negotiations, Philip succeeded in extorting the expenses for his armament from the dioceses of Würzburg, Bamberg, and Mainz, the latter bishopric also being compelled to recognize the validity of ecclesiastical jurisdiction in Hessian and Saxon territory until the emperor or a Christian council should decide to the contrary.

The condition of affairs was, however, very unfavorable to Philip, who might easily be charged with disturbing the peace of the empire, and at the second Diet of Speyer, in the spring of 1529, he was publicly ignored by the emperor. Nevertheless, he took an active part in uniting the Protestant representatives, as well as in preparing the celebrated protest of Speyer; and before leaving the city he succeeded in forming, on 22 April 1529, a secret understanding between Saxony, Hesse, Nuremberg, Strasburg, and Ulm.

Philip was especially anxious to prevent division over the subject of the Lord's Supper. Through him Huldrych Zwingli was invited to Germany, and Philip thus prepared the way for of the celebrated Marburg Colloquy. Although the attitude of the Wittenberg theologians frustrated his attempts to bring about harmonious relations, and although the situation was still further complicated by the position of Georg, Margrave of Brandenburg - Ansbach, who demanded a uniform confession and a uniform church order, Philip held that the differences between Strasburg and the followers of Luther in their sacramental theories admitted of adjustment, and that the erring could not scripturally be rejected and despised.

The result was that Philip was suspected of a tendency toward Zwinglianism. At the same time, the results of a conference with the elector of Saxony and with Margrave George at Schleiz (on 3 October), the anger of the emperor at receiving from Philip a statement of Protestant tenets, composed by the ex-Franciscan Lambert, and the landgrave's failure to secure any common action on the part of the Protestant powers regarding the approaching Turkish war, all tended to draw him closer to the Swiss and the Strasburg Reformers. He eagerly embraced Zwingli's plan of a great Protestant alliance to extend from the Adriatic to Denmark to keep the Holy Roman emperor from crossing into Germany. This association caused some coldness between himself and the followers of Luther at the Diet of Augsburg in 1530, especially when he propounded his irenic policy to Melanchthon and urged that all Protestants should stand together in demanding that a general council alone should decide concerning religious differences. This was supposed to be indicative of Zwinglianism, and Philip soon found it necessary to explain his exact position on the question of the Lord's Supper, whereupon he declared that he fully agreed with the Lutherans, but disapproved of persecuting the Swiss.

The arrival of the emperor put an end to these disputes for the time being; and when Charles V demanded that the Protestant representatives should take part in the procession of Corpus Christi, and that Protestant preaching should cease in the city, Philip bluntly refused to obey. He now sought in vain to secure a modification of the tenth article of the Augsburg Confession; but when the position of the Upper Germans was officially rejected, Philip left the diet directing his representatives manfully to uphold the Protestant position, and to keep general, not particular, interests constantly in view. At this time he offered Luther a refuge in his own territories, and began to cultivate close relations with Martin Bucer, whose comprehension of political questions constituted a common bond of sympathy between them, and who fully agreed with the landgrave on the importance of compromise measures in treating the controversy on the Lord's Supper.

In 1530 Philip was successful in accomplishing the purpose for which he had so long worked by securing the adhesion of the Protestant powers to the Schmalkaldic League, which was to protect their religious and secular interests against interference from the emperor. The landgrave and his ally, John Frederick, Elector of Saxony, became recognized leaders of this union of German princes and cities. Philip was thoroughly convinced that the Protestant cause depended on weakening of the Habsburgs both at home and abroad.

Before engaging in hostilities, Philip attempted to accomplish the ends of Protestant policy by peaceful means. He proposed a compromise on the subject of the confiscated church property, but at the same time he was untiring in providing for a possible, recourse to war, and cultivated diplomatic relations with any and all powers whom he knew to have anti - Habsburg interests. A peaceful turn was, however, given to the situation by the arrangements made at Nuremberg July 25, 1532, though this did not prevent Philip from preparing for a future struggle.

He was untiring in trying to draw new allies into the league against Charles V and Ferdinand, who had been invested with the duchy of Württemberg; the battle of Lauffen (May 13, 1534) cost Ferdinand his newly acquired possession; and Philip was now recognized as the hero of the day, and his victory as the victory of the Schmalkald League. In the years following, this coalition became one of the most important factors in European politics, largely through the influence of Philip, who lost no opportunity of furthering the Protestant cause. Its alliance was sought by both France and England; it was extended for a period of ten years in 1535; and new members were added to it.

On the other hand, the struggle between the two Protestant factions injured the advancement of their mutual interests, and Bucer, encouraged by Philip, was accordingly occupied in the attempt to bring Protestants together on a common religious platform, the result being the Wittenberg Concord. The emperor's fears as to the political purpose of the league were, for the time being, set at rest; but at the same time a council which should include representatives of the pope was rejected; and measures were taken to secure the permanence of the Protestant cause in the future. In 1538 – 39 the relations between Roman Catholics and Protestants became strained almost to the breaking point, and war was averted only by the Frankfort Respite. The Protestants, however, failed to avail themselves of their opportunities, largely through the extreme docility and pliability of Philip.

This unexpected course of the Protestant leader was largely conditioned by two factors: he was weakened by a licentious life, and his marital relations were about to bring scandal on all Protestantism. Within a few weeks of his 1523 marriage to the unattractive and sickly Christine of Saxony, who was also alleged to be an immoderate drinker, Philip committed adultery; and as early as 1526 he began to consider the permissibility of bigamy. According to Martin Luther, he lived "constantly in a state of adultery and fornication."

He accordingly wrote Luther for his opinion, alleging as a precedent the polygamy of the patriarchs; but Luther replied that it was not enough for a Christian to consider the acts of the patriarchs, but that he, like the patriarchs, must have special divine sanction. Since, however, such sanction was lacking in the present case, Luther advised against such a marriage, especially for Christians, unless there was extreme necessity, as, for example, if the wife was leprous, or abnormal in other respects. Despite this discouragement, Philip gave up neither his project nor a life of sensuality which kept him for years from receiving communion.

He was affected by Melanchthon's opinion concerning the case of Henry VIII, where the Reformer had proposed that the king's difficulty could be solved by his taking a second wife better than by his divorcing the first one. To strengthen his position, there were Luther's own statements in his sermons on Genesis, as well as historical precedents which proved to his satisfaction that it was impossible for anything to be un-Christian that God had not punished in the case of the patriarchs, who in the New Testament were held up as models of faith. It was during an illness due to his excesses that the thought of taking a second wife became a fixed purpose.

It seemed to him to be the only salve for his troubled conscience, and the only hope of moral improvement open to him. He accordingly proposed to marry the daughter of one of his sister's ladies - in - waiting,Margarethe von der Saale. While the landgrave had no scruples whatever, Margarethe was unwilling to take the step unless they had the approval of the theologians and the consent of the prince elector of Saxony and of Duke Maurice. Philip easily gained his first wife's consent to the marriage. Bucer, who was strongly influenced by political arguments, was won over by the landgrave's threat to ally himself with the emperor if he did not secure the consent of the theologians to the marriage; and the Wittenberg divines were worked upon by the plea of the prince's ethical necessity.

Thus the "secret advice of a confessor" was won from Luther and Melanchthon (Dec. 10, 1539), neither of them knowing that the bigamous wife had already been chosen. Bucer and Melanchthon were now summoned, without any reason being assigned, to Rotenburg an der Fulda, where, on March 4, 1540, Philip and Margarethe were united. The time was particularly inauspicious for any scandal affecting the Protestants, for the emperor, who had rejected the Frankfort Respite, was about to invade Germany. A few weeks later, however, the whole matter was revealed by Philip's sister, and the scandal caused a painful impression throughout Germany. Some of Philip's allies refused to serve under him; and Luther, under the plea that it was a matter of advice given in the confessional, refused to acknowledge his part in the marriage.

This event had affected the whole political situation. Even while the marriage question was occupying his attention, Philip was engaged in constructing far reaching plans for reforming the Church and for drawing together all the opponents of the house of Habsburg, though at the same time he did not give up hopes of reaching a religious compromise through diplomatic means. He was bitterly disgusted by the criticism directed against him, and feared that the law which he himself had enacted against adultery might be applied to his own case. In this state of mind he now determined to make his peace with the emperor on terms which would not involve desertion of the Protestant cause. He offered to observe neutrality regarding the imperial acquisition of the duchy of Cleves and to prevent a French alliance, on condition that the emperor would pardon him for all his opposition and violation of the imperial laws, though without direct mention of his bigamy.

The advances of Philip, though he declined to do anything prejudicial to the Protestant cause, were welcomed by the emperor; and, following Bucer's advice, the landgrave now proceeded to take active steps with the hope of establishing religious peace between the Roman Catholics and Protestants. Secure of the imperial favor, he agreed to appear at the Diet of Regensburg, and his presence there contributed to the direction which affairs took at the Regensburg religious colloquy, in which Melanchthon, Bucer, and Johannes Pistorius the elder represented the Protestant side. Philip was successful in securing the permission of the emperor to establish a university at Marburg; and in return for the concession of an amnesty, he agreed to stand by Charles against all his enemies, excepting Protestantism and the Schmalkald League, to make no alliances with France, England, or the duke of Cleves, and to prevent the admission of these powers into the Schmalkald League.

On the other hand, the emperor agreed not to attack him in case there was a common war against all Protestants. These arrangements for special terms led to the collapse of Philip's position as leader of the Protestant party. He had become an object of suspicion, and, although the league continued to remain in force, and gained some new adherents in succeeding years, its real power had departed. But while of the secular princes only Albrecht of Mecklenburg and Henry of Brunswick were still faithful to the Roman Catholic cause, and while united action might at the time easily have resulted in the triumph of Protestantism, there was no union; Duke Maurice and Joachim II of Brandenburg would not join the Schmalkald League; Cleves was successfully invaded by the imperial troops; and Protestantism was rigorously suppressed in Metz.

In 1543 the internal dissensions of the league compelled Philip to resign from its leadership, and to think seriously of dissolving it. He put his trust entirely in the emperor's good faith, agreeing to help him against both the French and the Turks. At the Diet of Speyer in 1544 he championed the emperor's policy with great eloquence; the bishop of Augsburg declared he must be inspired by the Holy Spirit; and Charles now intended to make him commander - in - chief in the next war against the Turks.

The situation was suddenly changed, however, and Philip was tardily forced again into the opposition, by the peace of Crespy, which opened his eyes to the danger threatening Protestantism. He prevented the Roman Catholic Duke Henry of Brunswick from taking forcible possession of his dominions; he unsuccessfully planned a new alliance with German princes against Austria, pledging its members to prevent the acceptance of the decrees of the projected Council of Trent; when this failed, he sought to secure the neutrality of Bavaria in a possible war against the Protestants; and he proposed a new Protestant alliance to take the place of the Schmalkald League.

But all this, like his projected coalition with the Swiss, was prevented by the jealousy prevailing between Duke Maurice and the elector of Saxony. Fearful of the success of these plans, the emperor invited Philip to an interview at Speyer. Philip spoke plainly in criticism of the emperor's policy, and it was soon evident that peace could not be preserved. Four months later (July 20, 1546) the imperial ban was declared against John Frederick and Philip as perjured rebels and traitors. The result was the Schmalkald war, the outcome of which was unfavorable to Protestant interests. The defeat at Mühlberg and the capture of the Elector John Frederick marked the fall of the Schmalkald League.

In despair Philip, who had been negotiating with the emperor for some time, agreed to throw himself on his mercy, on condition that his territorial rights should not be impaired and that he himself should not be imprisoned. These terms were disregarded, however, and on June 23, 1547, both the leaders of the famous league were taken to south Germany and held as captives.

The imprisonment of Philip brought the Church in Hesse into great trials and difficulties. It had previously been organized carefully by Philip and Bucer, and synods, presbyteries, and a system of discipline had been established. The country was thoroughly protestantized, though public worship still showed no uniformity, discipline was not strictly applied, and many sectaries existed. The Augsburg Interim was now introduced, sanctioning Roman Catholic practises and usages.

Philip himself wrote from prison to forward the acceptance of the Interim, especially as his liberty depended upon it. As long as the unrestricted preaching of the Gospel and the Protestant tenet of justification by faith were secured, other matters seemed to him of subordinate importance. He read Roman Catholic controversial literature, attended mass, and was much impressed by his study of the Fathers of the Church. The Hessian clergy, however, boldly opposed the introduction of the Interim and the government at Kassel refused to obey the landgrave's commands. Meanwhile his imprisonment was made still more bitter by the information which he received concerning conditions in Hesse, and the rigor of his confinement was increased after he had made an unsuccessful attempt to escape. It was not until 1552 that the Peace of Passau gave him his long desired freedom and that he was able, on September 12, 1552, to reenter his capital, Kassel.

Though Philip was now active in restoring order within his territories, new leaders — Maurice of Saxony and Christopher of Württemberg — had come to the fore. Philip no longer desired to assume the leadership of the Protestant party. All his energies were now directed toward finding a basis of agreement between Protestants and Roman Catholics. At his direction his theologians were prominent in the various conferences where representative Roman Catholics and Protestants assembled to attempt to find a working basis for reunion.

Philip was also much disturbed by the internal conflicts that arose after Luther's death between his followers and the disciples of Melanchthon. He was never wearied in urging the necessity of mutual toleration between Calvinists and Lutherans, and to the last cherished the hope of a great Protestant federation, so that, with this end in view, he cultivated friendly relations with French Protestants and with Elizabeth I of England.

Financial aid was given to the Huguenots, and Hessian troops fought side by side with them in the French religious civil wars, this policy contributing to the declaration of toleration at Amboise in March, 1563. He gave permanent form to the Hessian Church by the great agenda of 1566 – 67, and in his will, dated in 1562, urged his sons to maintain the Augsburg Confession and the Concord of Wittenberg, and at the same time to work on behalf of a reunion of Roman Catholics and Protestants if opportunity and circumstances should permit.