He was not yet thirteen years of age when his father died, so his mother assumed the regency for a few years. In 1255, he married Margaret, the daughter of King Theobald I of Navarre and Margaret of the Bourbon. Frederick's father-in-law was the Count of Champagne as well, and marriage of Margaret with Frederick signified the Gallicization of Lorraine and the beginnings of tension between French and German influences which characterises its later history. When Joan I of Navarre, Margaret's niece, (the daughter of her brother, Henry I of Navarre), married, Philip the Fair, the future king of France, in 1284, the ties to France grew. The long-held loyalty of the dukes of Lorraine to the Holy Roman Emperor had waned in the first half of the thirteenth century and French influence was pervasive leading to its permanent attachment to France in 1766.
During Frederick's reign, he fought the bishops of Metz until Pope Clement IV excommunicated him and put his duchy under an interdict. In 1257, the electors of the Holy Roman Emperor met at Frankfurt to elect a replacement for the antiking William II, Count of Holland, who had died in 1256. The electors could not agree and some, called the "English Party," elected Richard, Earl of Cornwall, the brother of Henry III of England, and opponent of the Hohenstaufen, like William. Some, however, elected Alfonso X of Castile, who was the grandson of the Hohenstaufen king Philip, whose daughter Beatriz was Alfonso's mother. That longstanding support for the established imperial dynasty (the Salian, Supplinburger, Staufen, and, briefly, Welf) came through in Lorraine again and Frederick fell in line with the maternally Hohenstaufen Alfonso. The rivalry between the two kings led to little actual combat and with both dead, the electors chose Rudolf of Hapsburg in 1273, reestablishing the kingdom as a unity.
By his marriage to Margaret, he had the following issue: