Stewart was born on 13 July 1940 in Mirfield, in the West Riding of Yorkshire, England, to Gladys (née Barrowclough), a weaver and textile worker, and Alfred Stewart (1905–1980). He has two older brothers, Geoffrey (b. 1925) and Trevor (b. 1935). His parents did not give him a middle name, but he used the middle name "Hewes" professionally for a while in the 1980s.Stewart spent much of his childhood in Jarrow. He grew up in a poor household and suffered from domestic violence inflicted by his father, an experience which later influenced his political and ideological beliefs. Alfred Stewart had been a regimental sergeant major in the British Army during the Second World War, and worked as a general labourer and as a postman. As a result of his wartime experience during the Dunkirk evacuation, Stewart's father suffered from what was then known as combat fatigue (related to what is now known as post-traumatic stress disorder). In a 2008 interview, Stewart said:My father was a very potent individual, a very powerful man, who got what he wanted. It was said that when he strode onto the parade ground, birds stopped singing. It was many, many years before I realised how my father inserted himself into my work. I've grown a moustache for Macbeth. My father didn't have one, but when I looked in the mirror just before I went on stage I saw my father's face staring straight back at me.Stewart attended Crowlees Church of England Junior and Infants School. He attributes his acting career to his English teacher, Cecil Dormand, who "put a copy of Shakespeare in my hand [and] said, 'Now get up on your feet and perform'." In 1951, aged 11, Stewart entered Mirfield Secondary Modern School, where he continued to study drama. Around the same time he met the actor Brian Blessed at a Mytholmroyd drama course, and the two have been friends ever since.At the age of 15, Stewart left school and increased his participation in local theatre. He gained a job as a newspaper reporter and obituary writer at the Mirfield & District Reporter, but after a year his employer gave him an ultimatum to choose acting or journalism, and he left the job. His brother tells the story that Stewart was attending rehearsals during work time and then inventing the stories he reported. Stewart also trained as a boxer. He has said that acting served as a means of self-expression in his youth. Both he and his friend Blessed later received grants to attend the Bristol Old Vic Theatre School.