After two years of didactic career at Blaj, as Professor of Philosophy and Church History, in 1807 he was appointed parish and protopop of Cluj.

He was archpriest of Cluj and, after 1829, secretary of the bishop of Făgăraş-Alba Iulia Ioan Bob to who he succeeded on 23 August 1832.

Usually, his sermons were elaborated in Hungarian, Ioan Lemeni being seriously criticized by a part of Romanian historians who ignored the specific historical context from that time.

In 1845 after a long and bitter dispute, Ioan Lemeni dismissed Simion Bărnuțiu from Blaj.

Together with the Orthodox Bishop Andrei Şaguna he had a role in the Hungarian Revolution of 1848 supporting the union of Transylvania with Hungary and so opposing the Austrian government.