After falling out with King Charles, Kettil Karlsson was subsequently elected Lord Protector and Regent (riksföreståndare) of Sweden from 26 December 1464 to his death.

On a subsequent journey to Mantua, where the Bishop-elect also served as diplomat to the Holy See on behalf of King Christian, Pope Pius II granted the confirmation and dispensation on 24 September 1459.

His relatives gathered their forces in the northern provinces of Västmanland, Dalecarlia and Uppland, where resistance among the farmers and miners against Christian's tax and foreign trade policies was strong.

A subsequent attempt by the unionist Lord High Constable Ture Turesson Bielke to land troops in Västmanland was defeated by Kettil Karlsson's militia from Rekarne at Kvicksund.

A Riksmöte called by Bishop Kettil and the separatist party recalled the exiled King Charles Canutesson, who brought a fleet and mercenary troops.

Meanwhile, Archbishop Jöns Bengtsson had been released from Danish captivity due to political pressure from the Church and abroad, reconciling with King Christian.

Kettil Karlsson was elected Lord Protector and Regent of Sweden on 26 December 1464, with Jöns Bengtsson as co-ruler, and on 30 January 1465 King Charles abdicated, instead receiving the castles of Raseborg and Korsholm in Finland.

Jöns Bengtsson was deposed and replaced as Regent by the Privy Councillor Erik Axelsson Tott in 1466, who in 1467 brought Charles Canutesson back as King for a third regency.