Thomas Andrew Millar was born in Glasgow, Scotland on 3 December 1880 and was articled to John Baird (1798-1859) and James Thomson (1835-1905) of Baird & Thomson from 1898 to 1902. He also attended Glasgow School of Art. From 1902 to 1904 he was employed as an assistant to James Miller (1861-1947).
Millar commenced independent practice as an architect in Glasgow on 1905 [or 1906 - sources differ], and from 1905 [or 1906] to 1912 was in partnership with Alexander McInnes Gardner (1878-1934) as Gardner & Millar. Millar was elected a Licentiate of the Royal Institute of British Architects (LRIBA) in 1911. He was also a member Glasgow Institute of Architects.
Following military service in World War One, he returned to Glasgow where he resumed practice as an architect, however in late 1921 he fell victim of the influenza pandemic and died in Glasgow on 25 January 1922.
Directory of British Architects 1834-1914. Compiled by Antonia Brodie, et al. Volume 2: L-Z. London; New York: British Architectural Library, Royal Institute of British Architects/Continuum, 2001