Born Kathleen Daly in Limerick, she was married to Tom Clarke, signatory of the Proclamation of the Irish Republic, one of those executed for his part in the Easter Rising in 1916. She preferred to be known as Caitlín Bean Uí Chléirigh (Mrs Tom Clarke) and had this inscription on her headstone. Tom Clarke had met her uncle, John Daly, while in prison, and married Kathleen, 21 years his junior, on his release in 1898. Her younger brother Edward Daly was also executed for taking part in the rising.
After her marriage she became active in politics was a founder of Cumann na mBan in 1914.
She was elected unopposed as a Sinn Féin TD to the Second Dáil in the May 1921 elections. She spoke against the Anglo-Irish Treaty in the Dáil debates in December 1921 and January 1922. She failed to be re-elected in the 1922 general election but was re-elected to the short-lived 5th Dáil in the June 1927 election. She again lost her seat in the September 1927 election and did not regain it. She contested the 1948 general election on behalf of Clann na Poblachta.
Following her failure to be elected to the Dáil in 1927 she was elected to Seanad Éireann in 1928 and retained her her seat in two subsequent elections until it was abolished in 1936. She was Lord Mayor of Dublin from 1939–1941. Following her death aged 94 in 1972 she received the rare honour of a state funeral.