Backus was acting on radio as early as 1940, playing the role of millionaire aviator Dexter Hayes on Society Girl on CBS.

He had an extensive career and worked steadily in Hollywood over five decades, often portraying characters with an "upper-crust", New England-like air, much like his best-known role, Thurston Howell III on Gilligan's Island.
He appeared in (and narrated) A Dangerous Profession (1949); Deadline – U.S.A. (1951) with Humphrey Bogart; Pat and Mike (1952) with Spencer Tracy and Katharine Hepburn; Rebel Without a Cause (1955); The Pied Piper of Hamelin (1957); and It's a Mad, Mad, Mad, Mad World (1963).
He also made television appearances on The Beverly Hillbillies (1962).

Backus was the voice of the nearsighted cartoon character Mr. Magoo.
Years later, when Backus was a frequent talk show guest, he would recount the time Marilyn Monroe urgently beckoned him into her dressing room.
Henny Backus, Jim's wife, recalled the story: "Jim was in the 1952 film Don't Bother to Knock, with Marilyn Monroe.
He came home one night during the filming and told me that Miss Monroe in her most seductive breathy voice asked him to meet her in her dressing room.
His curiosity got the better of him and he went.
Once there, she exclaimed like an excited child, 'Do Mr. Magoo!'
And Jim did."

He frequently could be heard on primetime radio programs in the postwar era, including The Jack Benny Program, and he portrayed an exceedingly vain character named Hartley Benson on The Judy Canova Show on the CBS Radio Network, as well as a similar character named Hubert Updike on The Alan Young Show on the NBC Radio Network.
He also starred on the short-lived variety program The Jim Backus Show on the ABC Radio Network in 1957 and 1958, when that network changed its name to the American Broadcasting Network (ABN) and tried out a "Live and Lively" format of "Big Time Radio" with orchestras and audiences.
Backus costarred in the comedy show I Married Joan from 1952 to 1955, portraying the husband of Joan Davis.

In stark contrast to his usual affluent characters, he guest-starred on The Brady Bunch as an old gold prospector, a role he also played on a Gilligan's Island episode.
He also had a role in the final season episode "The Hustler" in which he plays Mike's boss, Mr. Matthews.

Backus appeared on Gilligan's Island for all three seasons of its run, 1964 to 1967, and later in reunion TV films made between 1978 and 1981.
By the third and final film, The Harlem Globetrotters on Gilligan's Island, Backus was suffering from Parkinson's disease and his participation was limited to a cameo appearance.
Backus also returned as the voice of Mr. Magoo in various revivals between 1964 and 1977, which included The Famous Adventures of Mr. Magoo and What's New, Mr. Magoo?.

In 1977, Backus appeared in "Never Con a Killer," the pilot for the ABC crime drama The Feather and Father Gang.
Backus was acting on radio as early as 1940, playing the role of millionaire aviator Dexter Hayes on Society Girl on CBS.
He had an extensive career and worked steadily in Hollywood over five decades, often portraying characters with an "upper-crust", New England-like air, much like his best-known role, Thurston Howell III on Gilligan's Island. He appeared in (and narrated) A Dangerous Profession (1949); Deadline – U.S.A. (1951) with Humphrey Bogart; Pat and Mike (1952) with Spencer Tracy and Katharine Hepburn; Rebel Without a Cause (1955); The Pied Piper of Hamelin (1957); and It's a Mad, Mad, Mad, Mad World (1963). He also made television appearances on The Beverly Hillbillies (1962).
Backus was the voice of the nearsighted cartoon character Mr. Magoo. Years later, when Backus was a frequent talk show guest, he would recount the time Marilyn Monroe urgently beckoned him into her dressing room. Henny Backus, Jim's wife, recalled the story: "Jim was in the 1952 film Don't Bother to Knock, with Marilyn Monroe. He came home one night during the filming and told me that Miss Monroe in her most seductive breathy voice asked him to meet her in her dressing room. His curiosity got the better of him and he went. Once there, she exclaimed like an excited child, 'Do Mr. Magoo!' And Jim did."
He frequently could be heard on primetime radio programs in the postwar era, including The Jack Benny Program, and he portrayed an exceedingly vain character named Hartley Benson on The Judy Canova Show on the CBS Radio Network, as well as a similar character named Hubert Updike on The Alan Young Show on the NBC Radio Network. He also starred on the short-lived variety program The Jim Backus Show on the ABC Radio Network in 1957 and 1958, when that network changed its name to the American Broadcasting Network (ABN) and tried out a "Live and Lively" format of "Big Time Radio" with orchestras and audiences. Backus costarred in the comedy show I Married Joan from 1952 to 1955, portraying the husband of Joan Davis.
In stark contrast to his usual affluent characters, he guest-starred on The Brady Bunch as an old gold prospector, a role he also played on a Gilligan's Island episode. He also had a role in the final season episode "The Hustler" in which he plays Mike's boss, Mr. Matthews.
Backus appeared on Gilligan's Island for all three seasons of its run, 1964 to 1967, and later in reunion TV films made between 1978 and 1981. By the third and final film, The Harlem Globetrotters on Gilligan's Island, Backus was suffering from Parkinson's disease and his participation was limited to a cameo appearance. Backus also returned as the voice of Mr. Magoo in various revivals between 1964 and 1977, which included The Famous Adventures of Mr. Magoo and What's New, Mr. Magoo?.
In 1977, Backus appeared in "Never Con a Killer," the pilot for the ABC crime drama The Feather and Father Gang.
Jim Backus