[1] MacManus was born in 1950 near Blacklion, a village in the north-west of County Cavan in Ireland, and moved to London in the 1960s to find work.

[2][3][4] Still based in Maugheraboy, MacManus has been involved in Irish Republican politics since the early 1970s and was secretary of the County Sligo Anti-H-Block Committee which campaigned in support of the 1980 and 1981 hunger strikes.

He became a member of the Sinn Féin Ard Comhairle (National Executive) in 1982 and remained there for over twenty years.

After the IRA ceasefire in 1994, MacManus was part of the first formal and publicly acknowledged Sinn Féin delegation to meet with the British government in over seventy years.

His eldest son, Joseph MacManus, was an Provisional IRA volunteer who was killed in a shoot-out against an off-duty UDR soldier in Belleek, County Fermanagh, in February 1992.