Tull acted in a few films including Mosquito Squadron (1969), Sex Farm (1973), and Parting Glances (1986), directed by Bill Sherwood.

On Broadway, he was a founding member of Tony Randall's National Actors' Theatre and appeared in Getting Married by George Bernard Shaw.

Tull is the first of only two people – the other being Simon Vance – to have recorded the entire Aubrey-Maturin series of nautical historical novels by Patrick O'Brian in complete and unabridged form.

O’Brian once expressed disapproval of a dramatic rendition of recorded novels ("To revert to my ideal reader: he would avoid obvious emotion, italics and exclamation marks like the plague – trying to put life into flat prose is as useful as flogging a dead horse").

His lively dramatization of the characters, especially Jack Aubrey and Stephen Maturin, and his comprehensive command of the dialects and tenor of the novels endeared him to many O’Brian fans.