Born near Thurles, Co Tipperary, Ireland, O’Shanassy and his wife Margaret arrived in Australia in November 1839. After initially buying a farm, they opened a drapery shop in Collins St, Melbourne in 1845.
O’Shanassy’s political career began the following year when he won a by-election to become a member of the Melbourne Council. In November he lost his seat thanks, at least in part, to lingering anti-Catholic sentiment after the ‘Orange’ riots in July of that year.
After becoming identified with popular causes such as opposition to any revival of transportation he won a seat in the first Legislative Council elections in September 1851. On March 11, 1857 he became premier, but this ministry collapsed after only seven weeks. He again became premier on March 10, 1858, leading a conservative government for the next 19 months.
O’Shanassy formed his third, strongest and most successful ministry in November 1861. This government was responsible for important reforms such as the Civil Service Act, which classified salaries and set out principles for promotion.
Though remembered as a great supporter of Catholic education, O’Shanassy warned against bringing old-world loyalties into a new land and said people should act as Australians in their adopted country.