Maurice was the fourth child but first son of the still Catholic Duke Henry IV and the Protestant Catherine of Mecklenburg - Schwerin.

In December 1532, Maurice, aged 11, came to live at the castle of his godfather Albert of Brandenburg, cardinal, archbishop of Magdeburg and archbishop of Mainz. During two years, he lived the reflective life of the cardinal until his uncle, the Duke George, demanded his return to his homeland and began the training of the later Saxonian Duke and educated him as a catholic. After 1536 Maurice's father was converted to the Protestant faith and the entire Duchy followed him; Henry and Catherine took the education of their son again into their hands. When Maurice was 18 years old, he left his parents and moved with his older cousin John Frederick I, who resided in Torgau and was despised by Maurice; this originated a strong hate between both. With a further cousin, the Landgrave Philip I of Hesse, whom he met in Dresden, Maurice connected, however, in a lifetime friendship.

After Maurice came of age, in 1539, his parents began to look for a wife for him. The favorite was Philip's eldest daughter, Agnes. The marriage plans threatened to fail, however, because of the illegal double marriage of the Landgrave. Without the knowledge of his parents, Maurice remained committed to his engagement with Agnes. The wedding, particularly disapproved by his mother, took place in Marburg on 9 January 1541. Letters from that time illustrate the strong mutual devotion of the couple. Together they had two children:

1. Anna (b. Dresden, 23 December 1544 – d. Dresden, 18 December 1577), married on 24 August 1561 to Prince William I of Orange - Nassau. They divorced in 1574.
2. Albert (b. Dresden, 28 November 1545 – d. Dresden, 12 April 1546).

On 18 August 1541 the Duke Henry died, and Maurice, as the eldest son, succeeded him as the Duke of Saxony and Head of the Albertine Line. He replaced most of his advisors, because they had been against his marriage with Agnes since the beginning. George von Carlowitz, one of the new confidants of the Duke, advised Maurice (in order to prevent a war with the Emperor Charles V and his brother Ferdinand, at the same time King of the Romans and his neighbour as King of Bohemia) not to endanger the continuation of the Protestant Movement.

Thus, he participated in the emperor's army in the war against the forces of Sultan Suleiman the Magnificent of the Ottoman Empire (1542), Duke William of Jülich-Cleves-Berg (1543), and King Francis I of France (1544). However, on the other hand, the Duke confiscated the properties of the Catholic Church in his lands. From the fortune of dissolved monasteries in his country Maurice donated the Prince Schools (Fürstenschulen) in Schulpforta (100 places), Meissen (60 places) and Grimma (70 places). Legal basis for this was the "New National Order" (Neue Landesordnung) from 1543.

Later, Maurice refused to join in the Protestant Schmalkaldic League, although the Landgrave Philip of Hesse, his friend and father-in-law, was the Leader of the League. As principal reason for this refusal of the membership is generally regarded his hate to his Ernestine cousin John Frederick I and the Imperial promise of the Saxon electorship, then held by John Frederick. During the Holy Week of 1542, a brother war almost erupted between them, because John Frederick occupied the jointly administered "Wurzener Country". A disagreement between Maurice and John Frederick had preceded over the use of the tax revenues from this area. The intervention of the Landgrave Philip of Hesse and Martin Luther prevented the war.

Due to the energetic persistence of Elector John Frederick in establishing the Evangelical Faith, the Emperor Charles V, on 20 July 1546, imposed the Imperial Ban (Reichsacht) over him, with agreement of the Catholic Imperial Estates, enforcement of which was laid on Maurice after the Wurzener Feud. The emperor tried in this way to drive a wedge still more deeply into the Protestant camp in order to prevent a further propagation of the Protestant Faith. In case of successful enforcement, Maurice hoped to be invested by the emperor with the Electorship. Maurice hesitated for a long time, since by this punitive actions his father-in-law Philip of Hesse would have been affected also. But when the brother of the emperor, Ferdinand I, himself wanted to begin a campaign against Electoral Saxony, he had to forestall that, in order not to lose to the Habsburgs the initiative in his own countries.

Maurice returned to Charles's camp. After initial successes — he occupied Electoral Saxony nearly without a fight — Maurice with his army was pressured by the Schmalkaldic League and retreated toward Bohemia. In the crucial Battle of Mühlberg at the Elbe, the Emperor and his brother Ferdinand, as well as Maurice defeated the Schmalkaldic League with the capture of Landgrave Philip and John Frederick. According to contemporary chronicles, all of this happened on one day, 24 April 1547. In order to escape being beheaded, John Frederick ceded the Electorate and sizable lands to Maurice in the Surrender of Wittemberg. Duke Maurice of Saxony was raised to the Electoral Dignity already briefly after the battle on 4 June 1547 in the field camp to the Elector of Saxony. The official appointment took place later, but at a high price: He had betrayed the Evangelical Faith and had brought his father-in-law, Philip of Hesse, into a hopeless situation. Maurice assured him that he would not be imprisoned, if he would surrender to the emperor. However, Philip was taken prisoner and exiled, after he had fallen on his knees before Charles V.

Maurice, insulted after these incidents by his compatriots as "Judas", was also disappointed by the emperor's attitude (because now Charles V tried to reintroduce Catholicism in the Empire's Protestant territories and the continued imprisonment of his father-in-law, Landgrave Philip of Hesse, whose freedom Charles V had guaranteed), he hid, however, his feelings from him up to the Diet of Augsburg on 25 February 1548, where the ceremony of the formal possession of Maurice as Elector of Saxony took place. Charles V, hoped, with his appointment as the Elector of Saxony, to terminate the splitting of the faith in the Empire with the assistance of the Emperor.

Commissioned to capture the rebellious Lutheran city of Magdeburg (1550), Maurice seized the occasion to raise an Army and signed anti-Habsburg compacts with France and Germany's Protestant princes.

In the Treaty of Chambord signed with the French King Henry II in January 1552 Maurice promised to the King money and weapon assistance for a campaign against Charles V. As a return, Henry was able to take four Imperial cities (Metz, Toul, Verdun and Cambrai) togteher with their dioceses, but Maurice had no right to have them.

In March 1552 the rebels overran southern German states, including parts of Austria, forcing the Emperor to flee and release Philip of Hesse. While Henry advanced up to the Rhine and occupied the promised Imperial lands, the emperor was surprised by the attack and fled over the Alps to the Carinthia Villach. In view of this success, Maurice quit his alliance with Henry II and negotiated with Charles's brother King Ferdinand I a treaty, which Charles agreed with reluctantly. With the Peace of Passau, signed in August 1552, the Lutheran position was provisionally guaranteed. As part of the Peace, his former opponents from the Schmalkaldic War, John Frederick I of Saxony and the Landgrave Philipp of Hesse, were released. The war was terminated in 1556 by Ferdinand I; the Imperial cities remained in French possession.

When Maurice returned to Saxony after the Peace of Passau, it was no longer the "Judas"; both Protestants and Catholics regarded him with equal respect. Also the emperor strived for peace in the Empire. Shortly thereafter, he campaigned against the Ottomans in Hungary. The Margrave Albert Alcibiades of Brandenburg-Kulmbach (who had rejected the Passau armistice) conquered the dioceses of Würzburg and Bamberg — under his control since eleven years before, after his former owner, John Frederick ceded them to him — as well as the Imperial city of Nuremberg. This was the beginning of the Second Margrave War, which ended only with the Peace of Augsburg of 1555.

In 1552 Maurice with the army of the Holy Roman Empire (11,000 men) march in Hungary. The Ottomans besieged Eger, but the Black Death broke out in Hungary, and Maurice did not dare to move on.

Albert Alcibiades was a former ally of Maurice, which fought in the Schmalkaldic War on his side. But now Maurice was allied with, among others, Ferdinand I, and was compelled to fight against Albert Alicibiades. On 9 July 1553 the Battle of Sievershausen took place in Lehrte. Maurice won the battle; however, he was hurt seriously by a shot into the abdomen from behind and succumbed two days later in the field camp at the age of 32. He was buried in the Freiberg Cathedral. In 1853, 300 years after the Battle, his death was commemorated with a monument. The 7.5 tons heavy granite originates from his homeland in Saxony.

Because Maurice died without surviving male issue, his brother Augustus succeeded him as Elector. He established in Dresden, shortly after the death of Maurice, the Maurice Monument (Moritzmonument), the first historical monument in Saxony.