He was elected unopposed as a
Sinn Féin MP for the
Carlow constituency at the
1918 general election. In January 1919, Sinn Féin MPs refused to recognise the
Parliament of the United Kingdom and instead assembled at the
Mansion House in
Dublin as a revolutionary parliament called
Dáil Éireann, though Lennon did not attend as he was in prison. He again elected unopposed for the
Carlow–Kilkenny constituency at the
1921 elections. He opposed the
Anglo-Irish Treaty and
voted against it. He stood unsuccessfully as an anti-Treaty Sinn Féin candidate at the
1922 general election. Following this Lennon was arrested, tried and sentenced to five years in prison for his part in the robbery of a bank at Bagenalstown, County Carlow. Still considering himself an Irish Republican in 1927, Lennon did not endorse
Fianna Fáil in either of the two general elections that year as he believed they had reneged on certain core Republican principles. Nevertheless, Lennon offered them tacit support during the
1932 general election. Lennon and the IMRA sought to promote a fusion of Social Credit ideas with fundamentalist Catholicism and fascistic
corporatism. When Alfred O'Rahilly became aware of Lennon's support of his ideas, O'Rahilly quickly distanced himself from Lennon and his extremist rhetoric. In 1947, he named in the
Irish Press as the Irish Monetary Reform Association nominee for the
Carlow–Kilkenny constituency at the
1948 general election for the party. However, he did not contest the election. A party colleague, William Milner, ran in the neighbouring
Laois–Offaly constituency. By 1948 the IRMA had become utterly split between Lennon and Flanagan when Flanagan sought to support candidates from
Clann na Talmhan for the
Seanad. Lennon and the IMRA "National Executive" claimed it was previously agreed that the IMRA would not support any candidates for the Seanad and that Flanaghan was now in breach of their constitution and should be expelled. Although Flanaghan was indeed expelled for his actions, the bulk of the membership sided with Flanagan, and walked with him into a new, separate organisation called the "Irish Monetary Reform Party". With Flanagan and his supporters continuing to enjoy political success, the original IMRA withered and died away. By 1955 Lennon had rejoined
Sinn Féin, and stood for them at the
1955 Irish local elections, to no success. Lennon died in Carlow on 13 August 1958. == Death ==