He then attended the College of the Venerable Bede at the University of Durham, but did not graduate.At 18, shortly after the end of World War II, Moore was conscripted for national service.He had also filmed a Maverick episode with Garner two seasons earlier in which Moore played a different character in a retooling of Richard Brinsley Sheridan's 1775 comedy of manners play entitled "The Rivals." In the course of the story, Moore's and Garner's characters switched names on a bet, with Moore consequently identifying himself as "Bret Maverick" through most of the episode.
On 21 September 1946, he was commissioned into the Royal Army Service Corps as a second lieutenant. Immediately prior to his national service, he studied for two terms at the Royal Academy of Dramatic Art, during which his fees were paid by film director Brian Desmond Hurst, who also used Moore as an extra in his film Trottie True.
At RADA, Moore was a classmate of his future Bond costar Lois Maxwell, the original Miss Moneypenny.
He signed another long-term contract to a studio, this time to Warner Bros.
His starring role in The Miracle (1959), a version of the play Das Mirakel for Warner Bros.
That same year, he played a supporting role in The King's Thief starring Ann Blyth, Edmund Purdom, David Niven and George Sanders, all of whom had larger roles than Moore.
In the 1956 film Diane, Moore was billed third again, this time under Lana Turner and Pedro Armendariz in a 16th-century period piece set in France with Moore playing Prince Henri, the future king.
In the early 1950s, Moore worked as a model, appearing in print advertisements for knitwear (earning him the amusing nickname "The Big Knit"), and a wide range of other products such as toothpaste – an element that many critics have used as typifying his lightweight credentials as an actor.
In his book Last Man Standing: Tales from Tinseltown, Moore states that his first television appearance was on 27 March 1949 in The Governess by Patrick Hamilton, a live broadcast (as usual in that era), and he played the minor part of Bob Drew.
He subsequently appeared as the questionable character "14 Karat John" in the two-part episode "Right Off the Boat" of the ABC/WB crime drama The Roaring 20s, with Rex Reason, John Dehner, Gary Vinson, and again Dorothy Provine, appearing in a similar role but with a different character name.
In the wake of The Alaskans, Moore was cast as Beau Maverick, an English-accented cousin of frontier gamblers Bret Maverick (James Garner), Bart Maverick (Jack Kelly) and Brent Maverick (Robert Colbert) in the much more successful ABC/WB western series Maverick.
Christopher Lee and John Schlesinger were among the show's guest stars and series regulars included Robert Brown (who in the 1980s would play M in several James Bond films) as the squire Gurth, Peter Gilmore as Waldo Ivanhoe, Andrew Keir as villainous Prince John, and Bruce Seton as noble King Richard.