His most important domestic reform was the abolition in 1702 of the so-called vornedskab, a kind of serfdom which had fallen on the peasants of Zealand in the Late Middle Ages. His efforts were largely in vain because of the introduction of adscription in 1733.

After the war, trade and culture flowered. The first Danish theatre, Lille Grönnegade was created and the great dramatist Ludvig Holberg began his career. Also the colonisation of Greenland was started by the missionary Hans Egede. Politically this period was marked by the king's connection to the Reventlows, the Holsteiner relatives of his last queen, and by his growing suspicion toward the old nobility.

During Frederick's rule Copenhagen was struck by two disasters: the plague of 1711, and the great fire of October 1728 which destroyed most of the medieval capital. Although the king had been persuaded by Ole Rømer to introduce the Gregorian calendar in Denmark - Norway in 1700, the astronomer's observations and calculations were among the treasures lost to the fire.

Frederik IV, having twice visited Italy, had two pleasure palaces built in the Italian baroque style: Frederiksberg Palace and Fredensborg Palace, both considered monuments to the conclusion of the Great Northern War.

Frederick was deemed a man of responsibility and industry — often regarded as the most intelligent of Denmark's absolute monarchs. He seems to have mastered the art of remaining independent of his ministers. Lacking all interest in academic knowledge, he was nevertheless a patron of culture, especially in art and architecture. His main weaknesses were probably pleasure seeking and womanising, which sometimes distracted him. He was the second to last Danish king who joined a morganatic marriage (the last was Frederick VII with Louise Rasmussen / Countess Danner).

His mother was Charlotte, daughter of William VI, Landgrave of Hesse - Kassel. Without divorcing his first queen, Louise of Mecklenburg - Güstrow whom he had wed 5 December 1695, Frederick married twice more, thereby committing bigamy; in 1703, he married Elisabeth Helene von Vieregg (d.1704), and the second time, Frederick carried off the 19 year old Countess Anne Sophie Reventlow from her home in Clausholm near Randers on 26 June 1712 and secretly wed her at Skanderborg. At that time he accorded her the title "Duchess of Schleswig" (derived from one of his own subsidiary titles). Three weeks after Queen Louise's death in Copenhagen on 4 April 1721, he married her again, this time declaring her queen (the only wife of an hereditary Danish king to bear that title who was not a princess by birth). Of the nine children born to him of these three wives, only two survived to adulthood, Christian VI and princess Charlotte - Amalia, both from the first marriage. Among his other lovers were most notably Charlotte Helene von Schindel.

Nonetheless, much of the king's life was spent in strife with kinsmen. Two of his first cousins, Charles XII of Sweden and Frederick IV, Duke of Holstein - Gottorp (the three men were the grandsons of Frederick III of Denmark), had waged war upon his father jointly. Initially defeated by the Swedes and forced to recognize the independence of Holstein - Gottorp, Frederick finally drove the next duke of Holstein - Gottorp, Duke Charles Frederick (who was Frederick IV's first cousin once removed) out of Schleswig in 1713, and avoided the revenge contemplated by Charles Frederick's mother - in - law, Catherine I of Russia.

The Reventlows took advantage of their kinship to the king to aggrandize. The sister of Anna, the salonist Christine Sophie Holstein, was nicknamed Madame Chancellor because of her influence. Within a year of conferring the crown matrimonial on Countess Reventlow, Frederick also recognized as dynastic the issue of the morganatic marriages of two of his kinsmen, Duke Philip Ernest of Schleswig - Holstein - Glucksburg (1673 – 1729) and Duke Christian Charles of Schleswig - Holstein - Plön - Norburg (1674 – 1706), to non-royal nobles. The other Schleswig - Holstein dukes of the House of Oldenburg perceived their interests to be injured, and Frederick found himself embroiled in their complicated lawsuits and petitions to the Holy Roman Emperor. Also offended by the countess's elevation were King Frederick's younger, unmarried siblings, Princess Sophia Hedwig (1677 – 1735) and Prince Charles (1680 – 1729), who withdrew from Copenhagen to their own rival court at the handsomely re-modelled Vemmetofte Cloister (later a haven for dowerless damsels of the nobility).

During King Frederick's last years he was afflicted with weak health and private sorrows that inclined him toward Pietism. That form of faith would rise to prevalence during the reign of his son. On his death in 1730, Frederick IV was interred in Roskilde Cathedral.

King Frederick holds a memorable place in the social history of the city of Venice for a visit he made during the winter of 1708 - 09. The winter that season was particularly cold, so cold that the lagoon of Venice froze over, and the Venetians were able to walk from the city to the mainland. It was joked that the king of Denmark had brought the cold weather with him.