Ferdinand reigned as jure uxoris Count of Flanders and Hainaut from his marriage to Countess Joan, celebrated in Paris in 1212, until his death. He was born in Coimbra, and he was an Infante of Portugal as the fourth son of King Sancho I of Portugal and Dulce of Aragon.

The count of Flanders was the ruler or sub-ruler of the county of Flanders, beginning in the 9th century. Later, the title would be held for a time, by the rulers of the Holy Roman Empire and Spain. During the French Revolution, in 1790, the county of Flanders was annexed to France and ceased to exist. In the 19th century, the title was appropriated by Belgium and granted twice to younger sons of Belgian kings. The most recent holder died in 1983.