Starting his performing career directly after undergraduate studies, he won a position with the Greensboro Symphony in 1982. The next year he was offered the principal position of the Kennedy Center Opera House Orchestra in Washington, DC. The grueling demands of opera and ballet repertoire honed his skills as a versatile player. In 1989, he won the principal clarinet position of the Columbus Symphony in Ohio.

A noted orchestra among several giants in Ohio, the Columbus Symphony had its Carnegie Hall debut in 2001. The review was glowing.

For the past 16 years David has impressed audiences with his music making, both as orchestral and solo performer. Columbus Dispatch chief critic Barbara Zuck offered these comments in a 1994 review of Thomas' rendition of Rossini's Introduction, Theme and Variations:

"Thomas, ...has steadily grown in stature and confidence. Even so, I'm not sure anyone was prepared for the absolutely bravura display of virtuosity Thomas delivered last night. Who would have expected him to emerge as the clarinet equivalent of Cecilia Bartoli? I don't recall a bigger or better reception for any artist, anywhere."

From an April 30, 2005 review of the CSO in a concert of opera overtures and tenor arias, Zuck noted: "(Thomas) had as many great lines as the singer, and his brilliant performances once again reminded us how his playing has spoiled us over the years."