As a boy, Bentley learned several musical instruments, and while still in his teens was a staple on the Melbourne cabaret circuit as a comedian and singer, his act consisting of playing a few bars of music deliberately badly, interspersed with jokes and legitimate musical numbers. He made his first appearance on ABC Radio in the early 1930s and by 1938 had become a fairly prominent personality, notably on Wilfrid Thomas's show "Out of the Bag". In that year he moved to London and worked for the BBC. Newly married to Peta, he returned to Australia on the outbreak of war, and spent several years entertaining the troops in the Pacific theatre.
By 1946, he was one of Australia's highest-paid entertainers, and returned to Britain to try to re-establish himself in a much larger market. He joined up with writer Denis Norden and guested on many of the leading radio shows of the day. An appearance on Navy Mixture teamed him successfully with Jimmy Edwards, and indirectly led to the pairing of Denis Norden with Frank Muir, who was Edwards' writer. Muir and Norden together wrote Take It From Here (1948–60), with Edwards and Bentley as two of the three stars. The most memorable feature of Take It From Here was The Glums, with Edwards playing the slightly seedy Pa Glum and Bentley his terminally dim son, Ron. Bentley was thirteen years older than Edwards.
In 1951, during the run of Take It From Here, Bentley briefly returned to Australia to star in a ten-episode radio comedy series, Gently Bentley, commissioned to celebrate the silver jubilee of the ABC. In 1956, he starred in And So To Bentley, a sketch-format comedy show for the BBC, co-starring Peter Sellers. The show only lasted for one series, and the gently self-deprecating humor of Bentley was overshadowed by the charismatic Sellers. Both these shows were also written by Muir and Norden.
In 1960 he returned to Australia to play a sheep drover in The Sundowners, starring Robert Mitchum and Deborah Kerr. In the late 1960s he was back on BBC radio in the short run comedy series If You Had a Talking Picture of Me. In 1972 and 1974 Bentley was featured in the movies The Adventures of Barry McKenzie and Barry McKenzie Holds His Own, derived from the Barry McKenzie comic strip in Private Eye. By 1974 he had largely retired, but briefly returned to the screen to appear in the 1978 season of Some Mothers Do 'Ave 'Em as Frank Spencer's granddad, fittingly since the hapless Spencer was in many ways a descendant of his Ron Glum character in TIFH.
His wife died in 1988, and Bentley died from complications from Alzheimer's Disease in 1995.
- Tamahine (1963)
- Frank Muir (1997). A Kentish Lad. Bantam Press, London. ISBN 0-593-03452-X. Frank Muir's autobiography.