Issac Butt (September 6,1813 - May 5,1879) was the founder and first leader of the Home Rule League, subsequently known as the Irish Parliamentary Party. He resigned the leadership in 1879 and was replaced by William Shaw, who in turn was replaced by Charles Stewart Parnell in 1880.

Butt began his career as a Tory politician on Dublin Corporation. A brilliant barrister, he defended Irish leader Daniel O'Connell in court. His experiences led him to move from being an Irish unionist and an Orangeman to becoming an Irish nationalist. This led to his involvement in Irish nationalist politics and the foundation of the Home Rule League.

He died in 1880 in Clonskeagh in Dublin.