Theophilus Allen was born in Acton, London, England on 10 July 1846 and was articled to William Mayhew (1818-1880) and Charles Joseph Knight from 1863 to 1867. After a period travelling in France and Italy, he commenced independent practice as an architect in London in 1869. From 1880 to 1884 he was in partnership with John Mackland (?-1901). He was also in partnership with his son, Theophilus Arthur Allen (1868-1931) from 1893.
Theophilus Allen was elected an Associate of the Royal Institute of British Architects (ARIBA) in 1874 and a Fellow of the Royal Institute of British Architects (FRIBA) in 1891. He retired in 1906.
His address was given as 7 John Street, Adelphi, London in 1869 and 1873; 14 Argyll Street, Regent Street, London in 1881 and 1884; 3 Duke Street, Adelphi, London and Hauyards, Chobham 1891. He died in Chobham, Surrey on 20 March 1929.
Note: because of the similarity in their names, some of the work attributed to Theophilus Allen may be by Theophilus Arthur Allen
Directory of British Architects 1834-1914. Compiled by Antonia Brodie, et al. Volume 1: A-K. London; New York: British Architectural Library, Royal Institute of British Architects/Continuum, 2001