Musically inclined from an early age, he began playing the accordion at 3 and took up the harmonica in his teens. A few years later, inspired by Django Reinhardt, a fellow Belgian, he began playing guitar, as well. By the end of World War II he had become a full-time musician.

In 1949, he shared the stage with Charlie Parker at the Paris Jazz Festival, and a year later he toured Europe as the guitarist in a sextet led by Benny Goodman. He moved to the United States in 1951 and eventually became a citizen.

From 1953 to 1959, he was a member of the British jazz pianist George Shearing’s popular quintet. He mostly played guitar with Mr. Shearing, but his harmonica work was featured on at least one number at every performance. It was also showcased on the handful of albums he recorded as a leader in those years.

After leaving the Shearing group, Mr. Thielemans became a busy studio musician, even spending a few years on staff at ABC. But he remained active in jazz, with the harmonica now his main instrument. He toured frequently, and occasionally recorded as the leader of a small group, for the rest of his life.

Most of his albums presented him in a straightforward jazz context, but late in his career they took on a more international color. On “The Brasil Project,” released in 1992, and a follow-up, released the next year, he collaborated with Milton Nascimento, Gilberto Gil and other prominent Brazilian artists. And on the 1998 album “Chez Toots” he returned to his roots, leading a group of French and Belgian musicians in a program of French songs.