On 21 March 1842, he resigned his appointment and in April they sailed for Port Phillip where he acquired Barfold station near Kyneton and a property in Mount Macedon districts becoming a large proprietor.

During his leadership the situation on the gold fields of Ballarat deteriorated culminating in the Battle of Eureka Stockade on 4 December 1854.

A subsequent Commission of Inquiry criticized the handling of the disturbances and resulted in a drastic reduction of police numbers.

Mitchell was minister for railways in the John O'Shanassy ministry from 30 December 1861 until the government was defeated on 27 June 1863 over land reform.

He was elected second President of the Victorian Legislative Council on 27 October 1870,[5] and carried out his duties with ability, decision and courtesy.