Thomas McGill Cassels was a Scottish architect active in the late-19th and early- to mid-20th centuries. From 1885 to 1890 he studied at Ayr Academy in Scotland and was articled to architect Allan Stevenson. He later moved to Glasgow, Scotland where he first worked as a draughtsman in the office of civil engineer Charles C. Lindsay and then as principal assistant to Peter Macgregor Chalmers. While in Glasgow he attended classes at Glasgow School of Art and the Glasgow and West of Scotland Technical College. He returned to Ayr, Scotland to Allan Stevenson's office, in 1895 first as managing assistant, and later, from around 1922, as partner. He was elected L.R.I.B.A. in 1911. The practice Allan Stevenson & Cassels which first formed around 1922-3 later merged in 1927 with Alexander Mair, becoming Allan Stevenson, Mair & Cassels. After Meir's departure in 1929 Cassels continued the practice by himself and reverted the name of the company back to Allan Stevenson & Cassels. In 1945 the practice was taken over by Duncan McCulloch.
Dictionary of Scottish Architects, 'Thomas McGill Cassels, DSA Architect Biography Report,<http://www.codexgeo.co.uk/dsa/architect_full.php?id=M000768 > [accessed 07 December 2007]