Švitrigaila was born to Algirdas, Grand Duke of Lithuania, and his second wife Uliana of Tver. His date of birth is unknown, but it is believed that he was the youngest or second youngest son of Algirdas. He first appeared in politics in October 1382 when he witnessed the Treaty of Dubysa between his elder brother Jogaila and the Teutonic Knights. Historians believe that would indicate that at the time Švitrigaila was no younger than 12 which would put his date of birth sometime before 1370. In a complaint submitted to the Council of Florence, Švitrigaila claimed that he and Jogaila were favorite sons of Algirdas. Before his death in 1377, Algirdas transferred his throne to Jogaila but made him swear to make Švitrigaila his heir. Jogaila's representatives did not outright deny the arrangement and instead claimed that it had been modified by mutual agreement between the brothers.