In the 1970s and 1980s, he continued touring and recording, appearing with musicians such as Oscar Peterson, Elis Regina, Caetano Veloso, Ella Fitzgerald, Ivan Lins, Sarah Vaughan, Bill Evans, Dizzy Gillespie, Kenny Werner, Pat Metheny, Jaco Pastorius, Mina Mazzini, Elis Regina, Quincy Jones, George Shearing, Natalie Cole, Billy Joel, Paul Simon, and Paquito D'Rivera.

Thielemans recorded the soundtracks for The Pawnbroker (1964), The Reivers (1969), Midnight Cowboy (1969), The Getaway (1972), Cinderella Liberty (1973), The Sugarland Express (1974) and Looking for Mr. Goodbar (1977).

"[9] During an interview in 1988, he recalled, "I guess I was born at the right time to live and adapt and be touched by the evolution in the jazz language.

In 1949 he joined a jam session in Paris with Sidney Bechet, Charlie Parker, Miles Davis,[10] Max Roach and others.

[11] He first heard the faster bebop style of jazz from records by Parker and Dizzy Gillespie after they had reached Belgium after the war.

[6] As his small collection of jazz records grew, the music of Benny Goodman and Lester Young began to impress him the most.

Not long after he returned to his home in Belgium, he received a letter inviting him to join Goodman's band while they toured in Europe.

[9] Although Thielemans was hired on as a guitarist, when Goodman's group debuted at the London Palladium, he played the harmonica due to union restrictions.

[12] Thielemans moved to the United States in 1952 where he was a member of Charlie Parker's All-Stars and worked with Miles Davis and Dinah Washington.

[6] He recorded with singers and musicians including Ella Fitzgerald,[4] Pat Metheny, Jaco Pastorius, Stephane Grappelli, J.J. Johnson, Oscar Peterson, Shirley Horn, Joe Pass, and jazz pianist Bill Evans, among others.

[6] Toots Thielemans wrote "Bluesette", a jazz standard,[5] which he performed on harmonica[16] or while playing the guitar and whistling in unison.

[9] Toots also wrote the ballad "Ladyfingers", which appeared on Herb Alpert and the Tijuana Brass's album Whipped Cream and Other Delights.

[19] In 1969 he recorded "Honeysuckle Rose Aquarela Do Brasil" with singer Elis Regina and performed with her on Swedish television special.

[20] During his career he performed on many film soundtracks, such as The Pawnbroker (1964),[6] Midnight Cowboy (1969),[6] The Getaway (1972), Turkish Delight (1973), Cinderella Liberty (1973), The Sugarland Express (1974),[6] The Yakuza (1974), Looking for Mr. Goodbar (1977), The Wiz (1978), Jean de Florette (1986), and French Kiss (1995).

[24] He performed with the bassist Jaco Pastorius,[25] and in 1983 he contributed to Billy Joel's album An Innocent Man, in the song, "Leave A Tender Moment Alone".

[31] And during the first Caspian Jazz and Blues Festival in Azerbaijan in 2002, he performed his recorded version of "Imagine", his tribute to its writer, John Lennon.

[34] On 23 January 2009, he joined guitarist Philip Catherine on stage at the Liberchies church (Belgium) in memory of the 100th anniversary of the birth of Django Reinhardt.

In 2012, the Jazz at Lincoln Center concerts in New York celebrated Thieleman's 90th birthday with, among others, Herbie Hancock, Eliane Elias, and Kenny Werner.

[4] After the announcement, the Netherlands-based jazz and pop orchestra Metropole Orkest, along with American musician Quincy Jones, performed at London's Royal Albert Hall in Thielemans' honor.

Thielemans received a joint honorary doctorate from the Université libre de Bruxelles and the Vrije Universiteit Brussel, Belgium.

In 2001, he was raised into the Belgian nobility by King Albert II and created Baron Thielemans for life, this in recognition of his contribution to music.

[51][52] With Jay Anderson With Brook Benton With Jay Berliner, Gene Bertoncini and Richard Resnicoff With The Brothers Johnson With Philip Catherine With Ray Charles With Natalie Cole With John Denver With Rick Derringer With Sheena Easton With Eliane Elias With Bill Evans With Michael Franks With Richard Galliano With Dizzy Gillespie With Lesley Gore With Urbie Green With Henry Gross With Lena Horne With Shirley Horn With James Ingram With Billy Joel With Quincy Jones With Fumio Karashima With James Last With Peggy Lee With Julian Lennon With Joe Lovano With Melanie With Pat Metheny With Laura Nyro With Sally Oldfield With Jaco Pastorius With Oscar Peterson With Lionel Richie With Diane Schuur With George Shearing and Dakota Staton With George Shearing With Paul Simon With Frank Sinatra With Sivuca With James Taylor With Sarah Vaughan With Vanessa Williams With Aziza Mustafa Zadeh