He was the son of Count William II (1227-1256), who was elected Holy Roman King of the Holy Roman Empire in 1248, and was murdered in 1256 by Frisians when Floris was just two years old. First his uncle, then his aunt, and, after the battle of Reimerswaal (fought over custody of Holland) in 1263, Otto II of Guelders served as his guardians until he was twelve years old and considered capable of administrating Holland himself.
In 1272 he unsuccessfully attacked the Frisians in a first attempt to retrieve the body of his father. In 1274 he faced an uprising by nobles led by the powerful lords Gijsbrecht IV of Amstel and Hendrik of Woerden, who held lands in the north of the adjacent bishopric of Utrecht (the area of Amsterdam) at the expense of the bishop. He assisted the weak bishop, who would become dependent on Holland's support, and eventually added the lands of the rebellious lords to Holland in 1279. In 1282 he again attacked the troublesome Frisians in the north, defeating them at the battle of Vronen, and succeeded in retrieving the body of his father. After a campaign in 1287-1288 he finally defeated the Frisians. In the meantime he had received Zeeland-bewester-Schelde (the area that controls access to the Scheldt river) as a loan from the Holy Roman King in 1287, but the local nobility sided with the count of Flanders who invaded in 1290. Floris arranged a meeting with count Guy of Flanders, but he was taken prisoner and was forced to abandon his claims and then set free.
Floris immediately wanted to resume war, but King Edward I of England, who had an interest in access to the great rivers for wool and other English goods, convinced Floris to stop hostilities with Flanders. When in 1292 Floris claimed the throne of Scotland (his great-grandmother Ada being the sister of King William I of Scotland) he did not receive the expected support from Edward, but England did support his claims in a new, this time more successful, war on Flanders.
After Edward I moved his trade in wool from Dordrecht in Holland to Mechelen in Flanders, to gain Flanders's support against France, Floris switched sides to France in 1296. Edward I now prohibited all English trade on Holland and conspired with count Guy of Flanders to have Floris kidnapped and taken to France. The humiliated lords Gijsbrecht IV of Amstel and Hendrik of Woerden enter the scene again as part of the conspiracy. Together with Gerard of Velzen they capture count Floris during a hunting party. The news of his capture spreads quickly and the small group of knights is stopped by an angry mob of local peasants. In panic Gerard of Velzen kills the count, and the knights flee. Gerard of Velzen is later captured and killed in Leiden.
The life and death of Floris V inspired songs, plays, books, and a television miniseries (starring Rutger Hauer) in the Netherlands. Best known is the play "Gijsbrecht van Aemstel" of 17th century playwright and poet Joost van den Vondel.
The nickname "Peasant God" was introduced after his death in the nobility, and was originally intended to be an insult. He earned the name because he behaved "as if he was the good lord himself with his peasants". He apparently knighted 40 peasants as members of the order of St. Jacob without permission of the church, provoking the anger of the church and of the 12 existing noble members of that knightly order. This story has no historical basis, just like another story that claims that Gerard of Velzen participated in the conspiracy because Floris raped his wife. What is certain is that Floris was remembered as a saint by the peasants of Holland, and that the "Peasant God" became a symbolic hero in the struggle for independence from Spain (1568-1648).