Gediminas was born in about 1275. Because written sources of the era are scarce, Gediminas' ancestry, early life, and assumption of the title of Grand Duke in ca. 1316 are obscure and continue to be the subject of scholarly debate. Various theories have claimed that Gediminas was either his predecessor Grand Duke Vytenis' son, his brother, his cousin, or his hostler. For several centuries only two versions of his origins circulated. Chronicles — written long after Gediminas' death by the Teutonic Knights, a long-standing enemy of Lithuania — claimed that Gediminas was a hostler to Vytenis; according to these chronicles, Gediminas killed his master and assumed the throne. Another version introduced in the Lithuanian Chronicles, which also appeared long after Gediminas' death, proclaimed that Gediminas was Vytenis' son. However, the two men were almost the same age, making this relationship unlikely.
Recent research indicates that Gediminias' ancestor may have been Skalmantas. In 1974 historian Jerzy Ochmański noted that Zadonshchina, a poem from the end of the 14th century, contains a line in which two sons of Algirdas name their ancestors: "We are two brothers – sons of Algirdas, and grandsons of Gediminas, and great-grandsons of Skalmantas." This discovery led to the belief that Skalmantas was the long-sought ancestor of the Gediminids. Ochmański posited that the poem skipped the generation represented by Butvydas, and jumped back to the unknown ancestor. Baranauskas disagrees, believing Skalmantas was Butvydas' brother rather than his father, and that Vytenis and Gediminas were therefore cousins.
Gediminas became the Grand Duke in 1316 at the age of 40 and ruled for 25 years.