Alex Maskey was born in Belfast in 1952. He was educated at St Patrick's Christian Brothers' Primary School (Donegall St. Belfast) and St Malachy's College, Belfast. He was interned twice during the 1970s.

Maskey was the first representative from Sinn Féin elected to Belfast City Council. In 2002, he became the first Councillor from his party to assume the position of Lord Mayor of Belfast. Maskey served on Council until October 2010.

Maskey was elected to the Northern Ireland Forum in 1996, but did not attend the Forum in accordance with Sinn Féin's policy of abstentionism. In 1998, Maskey was elected to the Northern Ireland Assembly, representing Sinn Féin. He was re-elected in 2003, 2007 and 2016. Maskey served on the Assembly's Finance and Environment Committee and as chair of the Social Development Committee.

Maskey served on the Northern Ireland Policing Board from 2007-2011. From 1994, he has been a member of the Sinn Féin Ard Chomhairle (National Executive Committee).