The son of Béla I of Hungary and the Polish princess Rycheza (Ryksa), Ladislas was born in exile. Returning to Hungary, he and his brother Géza refused to contest the throne against their cousin Salomon; however, they quarreled with him and drove him from the country (1073). Géza took the throne, and, on his death, in 1077, Ladislas succeeded him as king of Hungary.

Ladislas extended Hungary's frontier in Transylvania and occupied Croatia (1091) to protect the rights of his sister, the widow of Zvonimir, prince of Croatia. In the investiture struggle over the nomination and installation of bishops, Ladislas sided with the pope, though he also initiated a policy of reconciliation with the Holy Roman emperor Henry IV. Ladislas rooted out heathens in his dominions with severity and introduced Roman Catholicism to Croatia, founding the bishopric of Zagreb (1091). He introduced an elaborate legal code that brought order and prosperity to his dominions.

Ladislas died suddenly while preparing for the First Crusade. The ideal Hungarian knight, he was regarded by the nation as a saint long before his canonization.