Once worked as a bouncer in a brothel.
Was raised in a Catholic orphanage following his mother's death.
Attributed his low, husky voice to the time he contracted mumps as a pubescent 12 year-old and was silent for three weeks; another possible explanation was a fall from a tree. It was carefully maintained by a lifetime of heavy smoking and drinking.
Was considered a premier voiceover artiste, especially in the advertising world. Amongst the products Bill vocalised for were Pan Am Airways, Seiko watches, Cadbury's Flake, Denim aftershave ("for men who didn't have to try too hard") and famously the Carlsberg's "Probably the best lager... in the world" promotion, which he took on after Orson Welles demanded too much money to continue promoting the drink.
Has acted in both the James Bond Eon Franchise and the Doctor Who Franchise.
On 18 Jun 2009, BBC Radio 4 broadcast a 30-minute tribute "Bill Mitchell: The Man Who Wrestled Pumas... Probably" presented by Miriam Margolyes and featuring Christopher Sandford, G.B. Zoot Money, Nick Angel, Rob Townsend, Kenny Clayton, Xavier Russell, and Bill's daughter Amanda McAllister. Produced by John Leonard and Paul Hardy.