After studying at St. Mary's Christian Brothers Grammar School, Belfast and Queen's University, Belfast, Hanna became a solicitor, founding Francis Hanna and Co., specialising in personal injuries and trade union cases.
A Roman Catholic supportive of a united Ireland, Hanna joined the Nationalist Party and was elected to Belfast City Council.
In 1942, he joined James Collins in defecting to the Northern Ireland Labour Party (NILP), and in a 1946 by-election, he was elected for Belfast Central.
[citation needed] He was re-elected unopposed as an "Independent Labour" candidate at the 1949 Northern Ireland general election, and shortly afterwards became the vice-chairman of the new Northern Section of the Irish Labour Party.
In 1964, he was one of the original supporters of Unity, but he stood down at the 1965 Northern Ireland general election.