Thiman was born in Ashford, Kent. Largely self-taught, he was awarded an FRCO in 1921. From 1930 he was Professor of Harmony at the Royal Academy of Music and later, from 1956 to 1962, was Dean of the Faculty of Music at the University of London. From 1958, having moved from Park Chapel (a Congregational Church in Crouch End, later to join with Ferme Park Baptist Church to form a Union Church in the same district, currently (2011) pastored by a professionally qualified pianist), he was organist of the City Temple in London, a Congregational Church where he increased his renown as an improviser of great skill. He was a keen advocate of amateur music-making and in the 1960s was the conductor and Musical Director of the Purley Choral Society, performing his 'Spring Garland' in 1964. The choir changed its name to The Chandos Choir in 1969, and is still going strong (www.chandoschoir.com); they performed his beautiful 'Go, Lovely Rose' in 2012. A prolific composer of small-scale works, he wrote much educational music for piano and other instruments, as well as accessible music for church choirs, some of which is still performed. He is best remembered for his short passion cantata, "The Last Supper" (1930) which sets texts from the gospels of Matthew and John and hymns by St Thomas Aquinas, Charles Wesley and Johann Franck. It remains one of the rivals to Stainer’s The Crucifixion in the repertoire of less ambitious choirs and choral societies.
He was conductor of the Elysian Concert Society that performed at Hornsey Town Hall and other venues in London, and died in 1975.