Gardiner was born in Wimbledon, England, and he was a graduate of the Royal Academy of Dramatic Art.^[2] His parents wanted him to be an architect, but he insisted on a career as an actor.

Gardiner started as a super on stage and eventually became well known on the West End stage. "He appeared in British revues, plays and films before delighting Broadway audiences in 1935 with a wallpaper imitation act in At Home Abroad."^[2] His other Broadway credits include Little Glass Clock and An Evening with Beatrice Lillie.^[3]

He was also well known to radio listeners, and was known on the air for his amusing train and car noises.

Gardiner worked in almost 100 movies.^[1] He started film work in crowd scenes, making his big film break in 1927 the silent film The Lodger, by Alfred Hitchcock.

His Hollywood film debut came in 1936.^[2] During his career he was cast in numerous roles, often as a British butler. One of his most famous roles was that of Schultz in Charlie Chaplin's The Great Dictator. He also performed memorable turns as Beverly Carlton (a parody of Noël Coward) in The Man Who Came to Dinner, the spurned "almost-husband" in The Doctor Takes a Wife, Christmas in Connecticut and – one of his most memorable roles – in the Laurel and Hardy epic The Flying Deuces.

He made guest appearances on television sitcoms of the 1960s, including Fess Parker's ABC series, Mr. Smith Goes to Washington and Stanley Holloway's Our Man Higgins. He appeared in the 1964 Perry Mason episode "The Case of the Ugly Duckling", as business owner Albert Charity, and in an episode of Alfred Hitchcock Presents ("Banquo's Chair"). In 1966, he was featured on Green Acres as orchestra conductor Sir Geoffrey in the first-season episode "Culture". In 1968, Gardiner appeared as a butler in an episode of “The Monkees” titled “The Monkees Mind Their Manor”. His last major role was alongside Phyllis Diller in her 1966–1967 ABC series The Pruitts of Southampton. Also in 1967 he made a guest appearance on Petticoat Junction, in the episode "Uncle Joe and the Master Plan", as Gaylord Martindale. He played role of Mr. Maudlin in season 6, episode 19, "Dead as a Dude" of 77 Sunset Strip.

Gardiner recorded a curious and eccentric classic called "Trains", which was regularly played on the 1950s British radio programme Children's Favourites. This record consisted of a tipsy-sounding Gardiner reciting a monologue, which he first introduced in the 1935 Broadway revue At Home Abroad, about steam railway engines (which he claimed were 'livid beasts') and impersonating both the engines themselves and the sound of trains running on the track. This latter he famously characterised as 'diddly-dee, diddly-dum' to mimic the sound pattern as the four pairs of bogie wheels ran over joins between the lengths of track – a sound no longer heard since welded rail joins were introduced. "Trains" was released as a 78 and a 45 by English Decca Records (F 5278) which remained on catalogue into the 1970s. At the end of the record Gardiner signs off with "Well folks, that's all: back to the asylum." He was summoned to Buckingham Palace to give a performance in person.

Gardiner was married twice. He first married Wyn Richmond, a British actress, but they divorced. Later he married model Nadia Petrova.^[1]

Gardiner had a son out of wedlock with Jane Bagnato in Toronto, Canada: Reginald James "Jamie" Gardiner was born January 1, 1939. He left Jane and his son after three years to marry Nadia. Jamie's last name was changed to Williams at age 8, after his mother married Reginald Williams in 1947.

Gardiner died of a heart attack at his home in Westwood, California, on 7 July 1980. He was survived by his wife.^[1]

• Chance Acquaintance by John Van Druten (1927)
• A Present from Margate by Ian Hay (1933)

• Reginald Gardiner at IMDb
• Reginald Gardiner at the Internet Broadway Database  
• Reginald Gardiner at Find a Grave