Cathal Brendan O’Toole, painter, printmaker, and teacher, was born in Dublin, Ireland on September 2, 1904, but his family moved to Scotland in 1915. Trained as a sign painter, O’Toole decided to study fine art at the Glasgow School of Art.  At age 19 O’Toole was a Captain in the revolutionary Irish Republican Army, operating in Scotland and sending arms, money, and men to the Irish revolutionists in 1922. He studied at the St. Endas College in Ireland which was directed at the time by the Brothers Pierce, one of whom, Patrick Pierce was the First President of the Irish Republic and both of whom were shot after the rebellion of 1916.  O'Toole fought in the Irish Civil War against England and at 21 (1925) left the British Isles to come to the United States to paint.

In 1925, he moved to New York where he became a fairly successful commercial artist, but lost everything in the crash of 1929.  He decided to return to his study of art for the next six years in New York, where he studied at the Art Students League and at the National Academy of Design School under Kroll, Neilson, Olinsky and Covey. He received two Tiffany Foundation fellowships and, in 1934, he received a $1500.00 Pulitzer award which he used to help fund three years in the British Isles, France, and Switzerland. While in Paris, he studied painting with Andre Lhote and printmaking at Atelier 17 with Stanley William Hayter.

O'Toole returned to the U.S. in 1938 and began a teaching career. He taught drawing and painting at Fitch Junior College (1938-1941), lectured on drawing at Columbia University (1948-1949), and then taught art and became chairman of art department at Wilkes College (now Wilkes University) in Pennsylvania (1950-1959). He later moved to Rochester, New York where he worked as an art director in television until his retirement in 1971. 

O'Toole was a member of the Salmagundi Club in New York City and the Society of American Etchers. He became an associate of the National Academy of Design in 1939 and was elected a full Academician in 1944. He received an Arts and Letters Award in Art in 1941 from the American Academy of Arts and Letters. O'Toole was also a founding member of the Rockland Foundation (now the Rockland Center for the Arts) in Nyack, New York. His work is represented in the collections of the Herbert F. Johnson Museum of Art and the National Academy Museum.

Cathal O’Toole died on April 16, 1991, in Rochester, New York.