Connellan joined Sinn Féin in 1908[1] and was prominent in the Newry Sluagh.
[2] Later in life, he was active in the Gaelic League and was the Senior Vice President of the Ulster Council of the National Athletic and Cycling Association of Ireland.
[1] Connellan was elected to the Newry Board of Governors in 1920, serving until 1922.
[1] In 1949, Connellan was elected to the Northern Ireland House of Commons, representing South Down.
[3] He was also a member of Newry Urban District Council and the Chairman of the National Popular Front in 1964.