James Brennan was born in Dublin in 1837 and studied at the School of Art and at the Royal Hibernian Academy School. He went to London and studied under Owen Jones and Sir Matthew Digby Wyatt, assisting then with decoration of Pompeian and Roman courts of the Crystal Palace, built for the Great Exhibition of 1850. He returned to Dublin and taught at the Dublin Society's school. In 1855 he studied at the Training School in London, and subsequently taught in the School of Art in Bermingham, then at South Kensington in London until 1860. He also taught part-time in Liverpool, Taunton and Yarmouth. He was headmaster of the Cork School of Art from 1860 to 1889 and exhibited numerous paintings at the RHA between 1861 and 1906.

In 1889 Brennan was appointed headmaster of the Metropolitan School of Art in Dublin. There he played and important part in the development of the school and the advancement of crafts (particularly lace-making) and industrial art throughout Ireland. Strickland (1913) points out Brennan's personal qualities and popularity among the students. He died three years after his retirement in 1907.

Brennan painted mainly small pictures of cottage interiors and scenes of Irish peasant life such as the Committee of Inspection (1877).