Buchanan was born in Helensburgh, Dunbartonshire, Scotland, the son of Walter John Buchanan Sr (1865-1902), auctioneer, and his wife, Patricia, née McWatt (1860-1936). He was educated at the Glasgow Academy.
After a brief attempt to follow his late father's profession and a failure at acting in Glasgow, he came to London and became a music hall comedian under the name of Chump Buchanan and first appeared on the West End in September 1912 in the comic opera The Grass Widow at the Apollo Theatre. Hardship dogged him for a while before he became famous whilst on tour in Tonight's the Night. He produced and acted in his own plays both in London and New York.
Buchanan's health was not robust, and, to his bitter regret, he was declared unfit for military service in the First World War. He appeared with some success in West End shows during the war, attracting favourable notices as a "knut" in the mould of George Grossmith Jr, and achieved front rank stardom in André Charlot's 1921 revue A to Z, appearing with Gertrude Lawrence. Among his numbers in the show was Ivor Novello's "And Her Mother Came Too", which became Buchanan's signature song. The show transferred successfully to Broadway in 1924. For the rest of the 1920s and 1930s he was famous for "the seemingly lazy but most accomplished grace with which he sang, danced, flirted and joked his way through musical shows.... The tall figure, the elegant gestures, the friendly drawling voice, the general air of having a good time." During the Second World War he starred in his own musical production "It's Time to Dance", whose cast included Fred Emney. The musical show was based on a book by Douglas Furber and L. Arthur Rose, and was staged at the Lyric Theatre, Shaftesbury Avenue, London.
He made his film debut in the silent cinema, in 1917 and appeared in about three dozen films in his career. In 1938, Buchanan achieved the unusual feat of starring in the London stage musical This'll Make You Whistle while concurrently filming a film version. The film was released while the stage version was still running; thus the two productions competed with each other. Other starring roles included Monte Carlo (1930), Smash and Grab (1937) and The Gang's All Here (1939). He also produced several films including Happidrome (1943) and The Sky's the Limit (1938), which he also directed. He continued to work on Broadway and the West End and took roles in several Hollywood musicals, including The Band Wagon (1953), his best-known film, in which he plays camp theatre director Jeffrey Cordova opposite Fred Astaire and Cyd Charisse. He suffered from spinal arthritis, though this did not stop him from performing several dance numbers with Astaire in Band Wagon.
Buchanan's British stage appearances included A to Z, Battling Butler, Toni, Sunny, That's a Good Girl, Stand up and Sing, Mr Whittington, This'll Make You Whistle, Top Hat and Tails, The Last of Mrs Cheyney, Fine Feathers, Canaries Sometimes Sing, Don't Listen, Ladies!, Castle in the Air, King's Rhapsody and As Long as They're Happy. His first pantomime appearance (Christmas, 1940) was as "Buttons" in Cinderella.
His productions included The Women, The Body was Well Nourished, Waltz Without End, It's Time to Dance, A Murder for a Valentine, Treble Trouble and The Lady Asks for Help.
Buchanan's American stage appearances included: André Charlot's Revues, Charles B. Cochran's Wake Up and Dream, Pardon My English, Between the Devil and Harvey (1948).
Buchanan's Hollywood films included Paris, The Show of Shows (1929), Monte Carlo (1930) and The Band Wagon (1953).
His British films included Yes, Mr Brown (1933), Goodnight, Vienna (1932), That's a Good Girl (1933), Brewster's Millions (1935), Come Out of the Pantry (1935), When Knights Were Bold (1936), This'll Make You Whistle (1936), Smash and Grab (1937), The Sky's the Limit (1938), Break the News (1938), The Gang's All Here (1939), The Middle Watch (1940), Bulldog Sees It Through (1940), As Long as They're Happy (1955) and Josephine and Men (1955). He made one French film (bilingual), The Diary of Major Thompson (1955).
Buchanan was a frequent broadcaster on British radio, especially during the Second World War. Programmes included The Jack Buchanan Show and, in 1955, the hugely popular eight-part series Man About Town.
On 12 June 1928, Buchanan participated in the first-ever outside television broadcast, conducted by John Logie Baird.
Television appearances in the USA included Max Liebman's Spotlight in 1954 and The Ed Sullivan Show.
In a British tradition of actor-management, Buchanan frequently produced his own shows, many of which were premiered in the Alhambra Theatre, Glasgow. He was also heavily involved in the more commercial side of British show-business. He was responsible, with partners, for the building and ownership of the Leicester Square Theatre, London, and the Imperial in Brighton. He also controlled the Garrick Theatre in the West End of London and the King's Theatre in Hammersmith. Jack Buchanan Productions (in which his partners were J. Arthur Rank and Charles Woolf) owned Riverside Studios in Hammersmith.
He had been at school with the pioneer of television John Logie Baird and with him co-owned Television Limited, which manufactured and rented televisions.
Not all his business ventures were profitable, and at his death his estate was valued for probate (in 1958) at £24,489 (equivalent to £516,000 today).
Buchanan's image was that of the raffish eternal bachelor, but he was, unknown to most, married to Saffo Arnau in 1915. She was a singer. This marriage was annulled in 1920.
Later in life, he married Susan Bassett, an American, in 1947; he was her second husband. Through her he had a stepdaughter, Theo, who lived with him and his wife. He had no children of his own.
He had previously had a relationship with Australian actress Coral Browne, and during her meeting in Moscow with Soviet spy Guy Burgess in the late 1950s she informed Burgess, on mentioning Buchanan, that "we almost got married'. "And...?" "He jilted me." Burgess, previously at the British Foreign Office, had defected to Moscow a few years earlier, and one of the few mementoes of his earlier life that he had been able to keep was one 78rpm Jack Buchanan record—"Who?"—which, when Browne visited his Moscow flat, he played repeatedly. This event is portrayed in Alan Bennett's play An Englishman Abroad.
Like David Niven, Buchanan was renowned for his portrayal of the quintessential English gentleman on stage and screen, despite being a Scot. Buchanan also provided financial backing for another Scot, John Logie Baird, in Logie's work to develop mechanical television. Buchanan was legendary among his colleagues for his financial generosity to less prosperous actors and chorus performers. Sandy Wilson recalled that, each year during the running of the annual Grand National horse race, Buchanan would cancel that day's performance of his current musical and would charter an excursion train to the racecourse and back, supplying meals for the entire cast and crew of his show ... and even giving them £5 each for a "flutter" on the horse of their choice.
Buchanan died in London in 1957 from spinal cancer, when he was 67 years old.
For a number of years, British film exhibitors voted him among the top ten British stars at the box office via an annual poll in the Motion Picture Herald.1936 - 6th
1937 - 5th
1938 - 6th