Alban Maginness was born on 9 July 1950 to Alphonsus and Patricia Maginness. He was educated at St Malachy's College, Belfast, the University of Ulster and Queen's University Belfast. While at university, Maginness became involved in the non-violent protests organised by the Northern Ireland Civil Rights Association and participated in the Civil Rights March in Derry on 30th January 1972. He was called to the Northern Ireland Bar in 1976, and the Bar of Ireland in 1984.

Maginness was first elected to Belfast City Council in 1985, representing the Social Democratic and Labour Party (SDLP). Maginness was the first Nationalist to serve as Lord Mayor of Belfast.

Maginness was chairperson of the SDLP from 1985-1991. He was elected to the Northern Ireland Assembly in 1998, and subsequently re-elected in 2003, 2007 and 2011. Maginness served as Chairman of the Assembly's Regional Development Committee, Social Development Committee, and the Enterprise, Trade and Investment Committee.