A scion of a leading Swedish noble family, Charles joined the noble faction supporting the peasant revolt of 1436 against the rule of Erik of Pomerania, (Erik VII) king of the united realms of Denmark, Norway, and Sweden. Playing off the peasant, noble, and royal factions against one another, he was elected regent in 1438 and led in forcing Erik to relinquish his throne in 1439. When Christopher of Bavaria was elected king in 1441, Charles was compensated with several fiefs, including Finland, and after Christopher's death, in 1448, he became king.

Opposed to a return to the Danish-led northern union, Charles aimed at Swedish dominance in Scandinavia and defended his policies with ardent nationalist propaganda. From 1451 to 1457 he fought against the forces of the Danish king Christian I, who sought control over Sweden. Charles's domestic program, including reduction of the church's economic powers and the reclaiming of royal fiefs, antagonized an important faction of the nobles led by the Oxenstierna and Vasa families, who overthrew him in 1457 and elected Christian I king.

Charles was recalled in 1464 for a brief term and again in 1467, when the nationalist noble faction led by the Tott and Sture families gained the advantage in their civil war against the Oxenstiernas and their allies. He had become a mere figurehead by that time; the real power was exercised by the nobles' state council.