Hearn was admitted to the Victorian Bar in 1860, although he only occasionally practised as a barrister. In 1873, Hearn was appointed as the first Dean of the newly created Faculty of Law, lecturing in subjects such as constitutional law. In 1874 and 1877 he again stood unsuccessfully for parliament, evading the ban on professors running for election on the basis that as a dean, he had lost his professorial title. In 1878 he was finally elected to the Victorian Legislative Council, for Central Province. Hearn was regarded as a good politician, who held conservative views but was less concerned with party politics than he was with the technical business of making legislation, and by 1882 he was regarded as a leader in the Council.