Born Constance Gore-Booth, the daughter of baronet and explorer Sir Henry Gore-Booth, she lived as a child at the anglo-irish family's ancestral home, Lissadell House in County Sligo. Constance and her sister, Eva Gore-Booth, were close friends of the poet W. B. Yeats who frequently visited the house, and were influenced by his artistic and political ideas.
Constance studied art at the Slade School in London and then in Paris, where in 1893 she met and married artist Count Casimir Markiewicz. They settled in Dublin in 1903, where she became involved in radical politics through the sufraggette movement and in the Irish nationalist movement, joining Sinn Fein in 1908. In 1913 her husband moved to the Ukraine and never returned.
She took part in the 1916 Easter Rising and was sentenced to death by the British government. (The sentence was commuted to life imprisonment, and she was released under the amnesty of 1917.)
On 28 December 1918 she was elected as MP for the constituency of Dublin St Patrick's, making her the first woman elected to the House of Commons, but as a Sinn Fein member she declined as a matter of policy to take up her seat. She joined the independent Irish govenment in Dublin as Minister for Labour, and was imprisoned twice again by the British for her involvement.
She fought actively for the republican cause in the Irish Civil War, and joined Fianna Fail. She was elected as an MP to the Dáil Éireann in 1923 and 1927.