It is not known when he was born. His father was Jan z Kamenice, the secretary of king John of Bohemia. Brothers were Michael z Vlašime, Burgrave of Svojanov, and Pavel z Vlašime a z Jenstejna, Grand Chamberlain.
As of 1351, Jan Očko was the Bishop of Olomouc. His coat-of-arms was that of bishop and silver two Vulture heads gules (common with z Vlasime a z Jenstejna).
At that time, he became an advisor to Charles IV. He later accompanied Charles IV on his way to Italy in 1355. On July 12, 1364, he became the Archbishop of Prague, succeeding the dead Arnošt of Pardubice.
In 1366 he ordered the incarceration of Jan Milíč z Kroměříže for his preachings against Charles IV, whom he called the "Antichrist". Jan Milíč was later freed by Charles and remained in his favour.