His first appearances on stage was at a local outdoor history pageant as Tom Of Towngate when he was 9 years old. At the age of 12, he entered the local Secondary Modern School where he continued to study drama. He has said that "the greatest thing that ever happened to me" was after he read Shylock aloud in front of his class and his teacher told him, "Stewart, you're good at this. You should do it for a living."
At 15, he dropped out of school and increased his participation in local theater. He acquired a job as a news paper reporter, but after a year, his employer gave him an ultimatum to choose acting or journalism. He quit the job. His brother tells the story that Stewart would attend rehearsals during work time and then invent the stories he reported. Supposedly, this caught up with him the night of a large fire of which, when questioned by his boss, he knew nothing about.
At 16 he was a furniture salesman. And at 17, he registered in the Bristol Old Vic. He lost most of his hair by the age of 19 (alopecia runs in his family), but he successfully sold himself to theater producers, after performing an audition with and without a wig, as "two actors for the price of one!".
He joined the Royal Shakespeare Company in 1966 and then the Royal National Theatre in the early 1980s. Over the years, Stewart took roles in many major television series without ever becoming a household name. He appeared as Sejanus in I, Claudius and Karla in Tinker, Tailor, Soldier, Spy, and took the romantic male lead in the BBC adaptation of Mrs Gaskell's North and South (wearing a hairpiece).
He played the character Gurney Halleck in David Lynch's 1984 film version of Dune. His character was dramatically cut from the original release of the film due to editing made to make the immensely long film shorter. Much of this footage was restored on the television broadcast of the film on Fox Television.
In 1987 Stewart went to Los Angeles to star as Captain Jean-Luc Picard in Star Trek: The Next Generation (1987-1994). From 1994 he also portrayed Picard in the movie spin-offs Star Trek: Generations, Star Trek: First Contact, Star Trek: Insurrection, and Star Trek: Nemesis. His life was substantially changed by Star Trek, and he has been quoted as saying "It was almost entirely a blessing. It introduced me to a world I never expected to be a part of — celebrity, fame, financial success. It also gave me the chance to work with the finest group of people I've ever known."
In 1991, he performed his one-man-play adaptation of Charles Dickens' A Christmas Carol in which he performed the roles of all of the 40-plus characters himself. His radiant energy and marvelous performance was repeated the following year in 1992 and then 1993, 1994, 1996 and then again, to benefit September 11th charities in 2001. For his performances in this play, he has recieved the Drama Desk Award for Best Solo Performance in 1992 and the Lawrence Olivier Award for Best Entertainment for Solo Performance in 1994.
Stewart was knighted in December, 2000.
Although he has had a tremendous amount of success doing films, he loves the theatre more. He once said "Ingmar Bergman was once asked which he preferred and he said, 'I love making movies, but the theatre is my life.' That exactly sums it up for me, too."