Hardwicke started his television career in the 1970. He played Pat Grant in "Colditz". He then played Arthur in the sitcom "My Old Man". In 1978, Hardwicke played Bellcourt in the last episode of "The Sweeney". David Burke, who played Doctor Watson in "The Return of Sherlock Holmes" series, asked Hardwicke to take over the role. Hardwicke played this role for eight years, from 1986 to 1994. His portrayal of Watson was calmer than Holmes'. In 1989, Hardwicke played the role of Watson on the West End stage in "The Secret of Sherlock Holmes".