Olav Engelbrektsson's background and origin are not known with certainty. We know he was Norwegian, and most probably he belonged to the low nobility from Hålogaland.
He came to Trondheim around 1515, where he became the dean of the Cathedral Chapter House. Before this he had studied for years on the Continent, and he had been a Master of Arts at the University of Rostock. He may have been Norway's first university teacher! In Trondheim in 1519 he published (with the Cantor Peter Sigurdsson) the missal book Missale Nidrosiense, a milestone in Norwegian publishing history.
Olav was elected Archbishop in 1523. Difficult years followed. Olav Engelbrektsson worked hard to reinforce the independent role of Norway and his church in relation to the monarchy in Copenhagen. He actively supported royal candidates who steadfastly remained with the Catholic Church. However, as time passed, the Archbishop was forced to acknowledge that his enemies outnumbered his friends. Several of his most influential supporters adopted a pragmatic attitude in the church conflict.
In the conflicts that arose in the wake of the Reformation, he pursued a hard line but was eventually forced to realise that the battle had been lost. After living in the fortified castle Steinvikholmen for some time, he escaped from Norway in 1537. He died in the Netherlands the following year.
Olav was the last Catholic archbishop in Norway. The Reformation meant that the church, and thus Trondheim, lost much of the influence it had until then had in Norway.
Recommended reading: Erkebispestolens historie [The history of the archbishop chair]. Land og Kirke, 1955.