His parents, burgher Pietari Juusten and his wife Anna, owned their townhouse near the Blackfriars' monastery at Viborg.
Juusten was acting headmaster of the Viborg school 1541–1543, after which the bishop sent him to Germany, to study in several universities.
The king sent bishop Juusten as ambassador to Russia in 1569, where tsar Ivan IV the Terrible kept him as a prisoner for over two years.
The year he died, Paulus consecrated Laurentius Petri Gothus as archbishop of Uppsala.
[1] Juusten authored the Finnish-language catechism (1574), the tale of his Moscow travel, a Mass book (1575) and the Chronicle of Finnish bishops, Suomen piispainkronikka, Chronicon episcoporum finlandensium.