His flute solo on the band's 1967 hit single "Nights in White Satin" is regarded as one of progressive rock's defining moments.

[2] Thomas was born at an emergency maternity unit set up during the Second World War[3] in Lickhill Manor, Stourport-on-Severn, Worcestershire, England.

[9] Thomas and Pinder were later in a band called Krew Cats, formed in 1963, who played in Hamburg and other places in northern Germany.

[10] Thomas and Pinder then recruited guitarist Denny Laine, drummer Graeme Edge, and bassist Clint Warwick to form a new, blues-based band, The Moody Blues.

Thomas sang lead vocals on George and Ira Gershwin's "It Ain't Necessarily So" from the musical Porgy and Bess.

Although they initially tried to continue singing R&B covers and novelty tunes, they were confronted over this by an audience member, and with their finances deteriorating they made a conscious decision to focus only on their own original material.

[20] The album is regarded as a progressive rock landmark, and Thomas's flute solo on the single "Nights in White Satin" one of its defining moments.

Thomas stated that a number of his compositions on the band's earlier albums were made in a studio broom closet, with himself writing songs on a glockenspiel.

[23] In a 2015 interview Thomas said that he and Pinder had contributed backing vocals to the song "I Am the Walrus" by the Beatles, as well as providing harmonicas for "The Fool on the Hill".

Thomas started to become a more prolific writer for the group, penning songs such as "Legend of a Mind"—an ode to LSD guru and friend of the band, Timothy Leary, and a popular live favourite[19]—and "Dr. Livingstone, I Presume" for In Search of the Lost Chord,[25] and "Dear Diary" and "Lazy Day" for On the Threshold of a Dream, as well as co-writing "Are You Sitting Comfortably?"

Thomas wrote and sang "And the Tide Rushes In", reportedly written after having a row with his wife,[28] and was credited with co-writing the album's final track "The Balance" with Edge, while Pinder recited the story.

1 album, and Thomas wrote and sang "Our Guessing Game" and "Nice to Be Here", also singing a co-lead vocal with Pinder, Hayward and Lodge on Edge's "After You Came".

[32] Thomas released the albums From Mighty Oaks (1975)[33] and Hopes, Wishes and Dreams (1976)[34] after the band temporarily broke up in 1974.

After contributing "Sorry" and "I Am" (both on the 1983 album The Present) Thomas temporarily stopped writing new songs for the band, for reasons unknown.

Thomas is credited with tambourine, harmonica or saxophone on The Other Side of Life, but it is unknown how many, if any, instrumental contributions of his ended up on the released version of the album, and at this point he was largely relegated to the role of a backup singer.

On The Moody Blues' 1991 release Keys of the Kingdom, Thomas played a substantial role in the studio for the first time since 1983, writing "Celtic Sonant" and co-writing "Never Blame the Rainbows for the Rain" with Justin Hayward.

[42] The Moody Blues – consisting only of Hayward, Lodge and Edge (Edge being the only remaining original member) plus four long-serving touring band members, including Gordon Marshall on percussion and Norda Mullen who took over Thomas's flute parts – only released one further studio album, December, following his departure from the band.

It was also revealed that he had married again, to his longtime girlfriend Lee Lightle, in a ceremony at the Church of the Holy Cross in Mwnt, Ceredigion Wales, on 9 July 2009.

The set includes, with the two albums, a remastered quad version of "From Mighty Oaks", a new song "The Trouble With Memories", a previously unseen promo video of "High Above My Head" and an interview conducted by fellow Moody Blues founder Mike Pinder.

[48] In later years Thomas resumed flute playing with other musicians, one instance of which was for the song "L'urlo nelle ossa", on the 2016 album Eros & Thanatos by Italian band Syndone.

[49] He also played flute on the track "Simply Magic" on John Lodge's 2015 album 10,000 Light Years Ago[41] and recorded with Moody Bluegrass.