He was Director of Elections in the Anti H-Block campaign of 1981 when Kieran Doherty was elected as a TD for the Cavan–Monaghan constituency.
The Sligo West Ward Cumann of Sinn Féin is named the Joseph MacManus Cumann in honour of MacManus and there is an annual lecture given in his name which has been addressed by Caoimhghín Ó Caoláin, Pat Doherty, Pearse Doherty, Aengus O Snodaigh and Gerry Adams in recent years.