Frederick III, Duke of Lorraine should not be confused with Frederick III, Duke of Upper Lorraine.
| Frederick III | |
| Succession: | Duke of Lorraine |
| Reign: | 9 February 1251 - 31 December 1303 |
| Predecessor: | Matthias II, Duke of Lorraine |
| Successor: | Theobald II, Duke of Lorraine |
| Birth Date: | 1240 |
| Death Date: | 31 December 1303 |
| Spouse: | Margaret of Navarre |
| Issue: | Theobald II, Duke of Lorraine Matthias Frederick Frederick Gerard Isabella Catherine Agnes Margaret |
| House: | House of Lorraine |
| Father: | Matthias II, Duke of Lorraine |
| Mother: | Catherine of Limburg |
Frederick III (1240 – 31 December 1303) was the Duke of Lorraine from 1251 to his death. He was the only son and successor of Matthias II and Catherine of Limburg.
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 Bourbon. Frederick's father-in-law was the Count of Champagne as well, and the 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, after the elections following the death of King William of Holland resulted in the contested election of both Richard, Earl of Cornwall and Alfonso X of Castile, Frederick of Lorraine sided with Alfonso, who through his mother Beatrix was the grandson of the Hohenstaufen Philip of Swabia. The rivalry between the two kings led to little actual combat and after Richard's death the 1273 election of Rudolf of Habsburg and the subsequent withdrawal of Alfonso reestablished unity.
By his marriage to Margaret, he had the following issue: