Career
He was re-elected as Member of Parliament for the new Longford constituency at the 1918 general election. McGuinness was serving a prison term when he was elected to Westminster and among those who worked on his election campaign was Michael Collins. The election slogan for McGuinness at the time was "Put him in to get him out!"
In common with the other Sinn Féin MPs, he did not take his seat in the British House of Commons, sitting instead as a Territorial Decoration in the revolutionary First Dáil, where he was appointed as substitute Director of Trade and Commerce on 27 October 1919.
He was re-elected unopposed at the 1921 general election in the new Longford–Westmeath constituency.
He died before the 1922 general election. He voted in favour of the Anglo-Irish Treaty in January 1922.