Starting at age nine Casimir, received his education from Johannes Longinus (Jan Dlugosz) and Filippo Buonaccorsi, called Callimachus. When Casimir was thirteen he was offered the throne of Hungary by factions discontented with king Mattias Corvinus. Casimir, who was eager to defend the Cross against the Turks, accepted the call and went to Hungary to receive the crown. His uncle Ladislaus III, king of Poland and Hungary, had already been killed in 1444 in battle at Varna while defending Christianity against the Turks. Casimir was unsuccessful in his undertaking and returned as a fugitive. He again became the pupil of father Longinus in 1475. His father, king Casimir IV, had initiated him well into public affairs and when his brother Wladislaus ascended to the Bohemian throne, Casimir became heir-apparent to the throne of Poland. In 1479, the king went for five years to Lithuania and Casimir was placed in charge of Poland. From 1481 - 1483 he administered the state with great prudence and justice. His father tried to arrange marriage with a daughter of emperor Frederick III, but Casimir preferred to remain single. Due to his devout faith and weakened state by fasting, he subsequently developed severe lung problems, which he could not fight off. On a journey to Lithuania in 1484, he died at Grodno. His remains were interred at Vilnius.
Casimir lived and reigned with great justice and possessed great charm and character. Many miracles are ascribed to him. He was canonized by Vatican as Saint Casimir and is the patron saint of many countries, like Lithuania.
On June 11, 1948 Pope Pius XII named Casimir Jogailaitis the special patron of all youth.