He made his first stage appearance, alongside his parents, at the age of three. Following education at Great Barr School (where musician Steve Winwood was a classmate), Shaw graduated from the London Academy of Music and Dramatic Art. He served his apprenticeship in repertory at the Queen's Theatre, Hornchurch and the Bristol Old Vic, and began television work in 1967, making his TV debut as hippy student, Robert Croft, in Coronation Street. Afterwards he took key roles in the first revival of Look Back in Anger (Royal Court/Criterion, 1968) and in A Streetcar Named Desire (Piccadilly Theatre, 1974).
Despite an extensive body of theatre and television work, he is best known for his role as undercover detective Ray Doyle in the British television series The Professionals alongside Lewis Collins and Gordon Jackson. Despite the fame it brought him, Shaw claimed a dislike for the violent police series and his role in it.
He appeared with Lewis Collins in an episode of The New Avengers before they were cast in The Professionals. They played a pair of terrorists.
Shaw also appeared as a Welsh medical student, Huw Evans, in the television comedy series Doctor in the House — Martin Shaw's character of Huw Evans later returned in a subsequent "Doctor" series as a very nervous expectant father for the Doctor at Large episode Mother and Father Doing Well.
In the 1980s, Shaw spent most of his working time in the theatre. His roles include Elvis Presley in the critically-acclaimed Are You Lonesome Tonight? written by Alan Bleasdale. He also starred in a 1987 TV advert for the Vauxhall Cavalier.
He returned to TV in the 1990s, taking leading roles in Rhodes and the police series The Chief. In 2001, he took on the title role of BBC drama Judge John Deed. He also played detective Adam Dalgliesh, starring in P.D. James' Death in Holy Orders in 2003 and The Murder Room in 2005. Another notable role was his portrayal of British South Pole explorer Robert Falcon Scott in The Last Place On Earth.
In 2006 he narrated and appeared in a DVD chronicling the 'Merlins over Malta' project, which featured the return of a World War Two Supermarine Spitfire and Hawker Hurricane from Britain to Malta for the first time in 50 years.
In December 2006, he presented and appeared in the Discovery Channel Real Time TV series Martin Shaw: Aviators, produced by Twofour which followed the two-year restoration of his Boeing Stearman bi-plane after it had crashed in front of his eyes at Old Buckenham airfield in Norfolk. He fulfilled his lifetime's ambition in the six-part series by getting to take the controls of a Spitfire owned by Maurice Bayliss; and he screamed down the runway at Cranfield in a English Electric Lightning owned by Russell Carpenter. It wasn't allowed to take off, but did reach 150mph in three seconds. Martin Shaw also compared notes with Wing Cdr Ken Wallis, the nonagenarian builder and developer of the modern autogyro.
Shaw has been married three times and divorced twice. He has three children by his first wife, actress Jill Allen whom he married in 1968, including son Joe Shaw who played a younger version of Martin's eponymous character in Rhodes. His other children Luke and Sophie are also actors. His second wife was former nurse turned alternative therapist Maggie Mansfield. Shaw was married to TV presenter, Vicky Kimm, who shared his love of flying. Shaw lived in a Quaker House in Norfolk, once owned by an ancestor of Abraham Lincoln. He also owns a crofter's cottage in Scotland. Shaw has been linked with Karen Da Silva, a 44-year-old yoga teacher and neighbour in his Norfolk village.. Shaw is an avid supporter of Aston Villa Football Club.