From 1980 to 1993, he was principal conductor of the Boston Pops Orchestra. He still has close ties with the Pops and the Boston Symphony Orchestra (BSO), which have much overlap and both perform out of Boston's Symphony Hall. He conducts several concerts with the Boston Pops every year, particularly during their Holiday Pops season. He also frequently enlists the Tanglewood Festival Chorus, the official chorus of the BSO, to sing choral music in his movie scores (such as Saving Private Ryan).
Williams has written various concert works, including concerti for flute, violin, trumpet and tuba.
He is an accomplished pianist, as can be heard in various scores in which he provides solos, as well as a handful of classical recordings.