Dermot O’Toole studied at the Metropolitan School of Art, Dublin, and Crawford Technical Institute and Crawford School of Art in Cork. Since 1933, he worked for various architectural firms in Dublin. Later, he joined the Office of Public Works and was one of the architects of Dublin Airport. Around 1945, he established his own firm, with his colleague Thomas Paul Kennedy, in central Dublin. From 1957, he worked on his own, eventually from his home in the small town of Dalkey near Dublin. In addition to private and commercial projects, he was engaged in urban and landscape planning. In 1944, he published a Planning Scheme for Ballycastle. The project of a sports park was not realized.