Walker made his first public broadcast at Shelsley Walsh hillclimb in 1948. He was given a recorded audition for the BBC at the 1949 Easter Monday Goodwood race. Walker later commentated on races alongside the tennis commentator Max Robertson, with his first radio broadcasting coming at the 1949 British Grand Prix for the BBC. He and Robertson were positioned at Stowe corner for the event. His debut television broadcast came in the same year when he commentated on hill-climbing at the Knatts Valley motorcycle venue in Kent. His first regular broadcasting work was on radio coverage of the Isle of Man annual Tourist Trophy motorcycle race alongside his father. Walker and his father were the single father and son sports commentary pair within the BBC from 1949 to 1962. After the death of his father in 1962, he became the BBC's chief motorcycling commentator.