Began his professional career in Jazz in Chicago, joining "The Malachi Thompson Quartet" in 1970, followed by occasional gigs with Muhal Abram's AACM Big Band. In recent years, began using his full name in order to avoid confusion with similar named musicians. Appearing with some of the greatest names in Jazz, his professional gigs since 1972 include Stanton Davis, Carter Jefferson, Andrew Cyrille, Kenny Drew, John Lewis, Harold Ousley, and Chet Baker. Has also performed as a sideman with Jimmy McGriff and Joe Henderson here in the United States. Although only 18 at the time, both McGriff and Henderson enlisted his sideman services on both concerts and recordings. After a 1977 move to Europe, he toured the Middle East, Africa, and the Far East performing extensively with Charles Tolliver, Art Taylor, Dizzy Gillespie, Sonny Stitt, Tony Scott, Malachi Thompson, and many others. Joined "The Art Taylor (Coltrane's first drummer) Quartet" in 1978, and stayed with it until 1984. Was then tapped by Charles Tolliver in 1980, continuing a fruitful relationship as a sideman till 1990.

"Birth Of The Cool" trombonist, Mike Zwerin recruited him for two tours in Africa in '80 and '81 respectively. Mike was also well known as a journalist for "The Village Voice", as well as music editor for "The Herald Tribune" and "The New York Times" before his death.  

Has performed with his own formations, "John Thomas & LIfeforce", "Serious Business", "The John D. Thomas Quartet", and "Extremely Serious Business" at festivals, concerts, and clubs throughout Europe, Africa, and the United States. Received the endorsement of the National Endowment of the Arts in 1980. Participated in its "Arts America Program", touring abroad under the auspices of the US Department of State, and remaining on its active list for the next ten years.

In 1986, his group "Extremely Serious Business", sponsored by the State Department toured Sub-Saharan Africa. Since returning to the United States in 1990, has appeared with his quartet, trio, and an updated version of his group "Extremely Serious Business", which performs his original compositions. It was also about this time, that he began a two year stint with the late organist Charles Earland.

1994 saw a move to Boston, where he performed regularly with different formations, including drummer Kenwood Dennard's "Real Thing". Since that time, Thomas continues work as a sideman and performs with his group "Extremely Serious Business". 2015 was the year of his latest release "Headwall" on  music pioneer producer and impresario Bernie Stolman's ESP-disk label. 

John, a.k.a. "JT", has long been associated with institutions in the academic world and held several teaching positions over the decades. He began at "The Jazz Lab" at the famous Gesamthochschule Duisburg under Dr. Ilse Storb in 1977 - now known as Merkatur University - and continued there till 1989. From there, went on to teach large and small ensembles, and instrumental lessons at the German Armed Forces School of Music in Hilden, mostly to members of different Jazz combos, dance orchestras for official state functions, and the famous Gunther Norris Air Force Big Band. Was simultaneously engaged as a docent at the prestigious Robert Schumann Institute - now Hochschule (Conservatory) - in Düsseldorf in Germany, and at the Jazz Studio School in Antwerp, Belgium.

In 1994 was appointed associate professor of guitar at the renown Berklee College of Music, where he served until 2012. He has also worked extensively at clinics and workshops from Belgium to South Africa. 

Dworp - Belgium, Soweto - South Africa, Niamey - Niger, Braunschweig - Germany, Linz - Austria, St. Dié - France, Remscheid - Germany, Salzburg - Austria, Burghausen - Germany, Torino - Italy, Püttlingen - Germany, Geneva - Switzerland, Avignon - France, Santa Clara - California, Neuhofen - Austria, Mamelodi - South Africa, Bassano - Italy, Port Elizabeth - South Africa, Graz - Austria, Durban - South Africa