Mansel Treharne Thomas OBE (12 June 1909 – 8 January 1986) was a Welsh composer and conductor, who worked mainly in South Wales. He was one of the most influential musicians of his generation, known as a composer, conductor and adjudicator. He was for many years employed by the BBC and promoted the careers of many composers and performers. He himself wrote vocal, choral (mixed, female, children’s and male voices), instrumental (solo and chamber), band and orchestral music, specialising in setting songs and poetry. Many of his orchestral and chamber music pieces are based on Welsh folk songs and dances.
He was born on 12 June 1909 in Pontygwaith near Tylorstown, Rhondda, in a house in Llywellyn Street, where a plaque was later placed by the Rhondda Civic Society. At the age of sixteen, he won a scholarship to the Royal Academy of Music, where he studied under Benjamin Dale.
He joined the BBC in 1936, but interrupted his career to serve in World War II.
From 1946 until 1965 he was principal conductor of the BBC Welsh Orchestra, now the BBC National Orchestra of Wales, and the BBC Welsh Chorus, but his career ended after he suffered a stroke in 1979. He retired to Monmouthshire and was co-founder of the Llantilio Crossenny Festival of Music and Drama.
He died at Gilwern, Monmouthshire in 1986, at the age of 76 and is buried at the church of St Mary's Church, Magor.
The Mansel Thomas Trust, based in Ponthir, was established in 1987 to commemorate the composer. It is concerned mainly with collecting his works and making them available to musicians.