The son of Irish socialist James Connolly and Lillie Connolly, he was involved in the Easter Rising in 1916, where he served in the GPO under his father. He joined the Socialist Party of Ireland in 1917.
Connolly traveled to Russia on several occasions in 1920–21 and formed a close association with Vladimir Lenin and was hugely influenced by the Soviet leader. He was a delegate to the Second Congress of the Communist International.
He helped form and became President of the first Communist Party of Ireland (CPI) in October 1921. He was editor of CPI newspaper, The Workers' Republic. He opposed the 1921 Anglo-Irish Treaty between the Irish Republican Army (IRA) and the British state and fought in the Civil War on the side of the republican forces. The CPI was the first Irish political party to oppose the Treaty and urged the IRA to adopt socialist policies to defeat the new Free State government. The CPI was dissolved in 1924 by the Comintern but in 1926, Connolly helped set up a second Marxist party, the Workers Party of Ireland. Connolly was the party leader and editor of its journal, The Hammer and Plough. This party too was dissolved in 1927.
Connolly joined the Irish Labour Party in 1928 and in 1934 participated in the last socialist initiative of Inter-War Ireland, the Irish Republican Congress. He was imprisoned twice in 1935. At the 1943 general election, Connolly was elected to the Dáil as a Labour Party Teachta Dála (TD) for Louth. He lost his seat at the 1944 general election, but was re-elected at the 1948 general election, before losing once more at the 1951 general election. Connolly was also financial secretary of the party from 1941–49.
Connolly entered something of a semi-retirement between the mid-1950s to mid-1960s, but in the late 1960s, he began a comeback. He was elected as party chairman in 1971 and held this position until 1978. Connolly also sat in the Irish Senate from 1975–77 on the Cultural and Educational Panel. He was a strong supporter of the Labour Party–Fine Gael coalition government that was in power from 1973–77. Connolly died in St Michael's hospital, Dún Laoghaire, in December 1980. He had both pneumonia and stomach cancer. Connolly is buried in Glasnevin Cemetery, Dublin.
- John Riddell (ed.), Workers of the World and Oppressed Peoples, Unite! Proceedings and Documents of the Second Congress, 1920: Volume 2. New York: Pathfinder Press, 1991; pg. 841.
- "Roderick Connolly". ElectionsIreland.org. Retrieved 15 December 2008.
- "Mr. Roderick Connolly". Oireachtas Members Database. Retrieved 15 December 2008.