Theo McNab was born in Dublin in 1940. He does not have any formal artistic training, instead he us mostly self-taught. Despite this his paintings, abstract and minimalist landscapes, are highly accomplished studies, executed in muted tones. His works often from a grid structure, similar to fellow Irish artist Charles Tyrrell, that are focused on the interplay of light and perspective within in this system. They are both depictions of the organic landscape and the geometric forms found within it.
McNab first exhibited his work in 1971 in Dublin, and had a one-man show in 1973. His work was shown in Rosc 80. He has represented Ireland at the prestigious international painting festival Cagnes-sûr-Mer in 1975, and has participated in group shows in California, England, Italy, Germany, Japan and China. He won the Scott Tallon Walker Prize at the Oireachtas Exhibition in 1976. He was head of Fine Arts at NCAD from 1988-2000 and was elected to membership of Aosdána, the Irish Association of Artists, in 1981. His work is held in the collections of the Irish Museum of Modern Art, Dublin City Gallery The Hugh Lane, and the University of Limerick Art Collection.