Frees was born Solomon Hersh Frees in Chicago, Illinois, on June 22, 1920; he grew up in the Albany Park neighborhood and attended Von Steuben Junior High School in Peoria. He had an unusually wide four-octave voice range that would enable him to voice everything from the thundering basso profundo of the unseen "Ghost Host" in the Haunted Mansion attraction at Disneyland in California and at Walt Disney World in Florida to the voice of the farmer who helps the Little Green Sprout (voiced by Ike Eisenmann) in the Green Giant vegetable commercials.

In the 1930s, Frees first appeared on vaudeville as an impressionist, under the name Buddy Green. He began his career on radio in 1942 and remained active for more than 40 years. During that time, he was involved in more than 250 films, cartoons and TV appearances; as was the case for many voice actors of the time, his appearances were often uncredited.

He appeared frequently on Hollywood radio series, including Escape, playing lead roles and alternating with william Conrad as the opening announcer of Suspense in the late 1940s, and parts on Gunsmoke (doing an impersonation of Howard McNear as Doc Adams for at least one episode, "The Cast"), and Crime Classics. One of his few starring roles in this medium was as Jethro Dumont/Green Lama in the 1949 series The Green Lama, as well as a syndicated anthology series The Player, in which Frees narrated and played all the parts.

Frees was often called upon in the 1950s and 1960s to "re-loop" the dialogue of other actors, often to correct for foreign accents, lack of English proficiency, or poor line readings by non-professionals. These dubs extended from a few lines to entire roles. This can be noticed rather clearly in the films Grand Prix (as Izo Yamura) and Midway where Frees reads for Toshiro Mifune's performances as Admiral Yamamoto; or in the film Some Like It Hot, in which Frees provides the voice of funeral Director Mozzarella as well as much of the falsetto voice for Tony Curtis' female character Josephine. Frees also dubbed the entire role of Eddie in the Disney film The Ugly Dachshund, replacing actor Dick Wessel, who had died of a sudden heart attack after completion of principal photography. Frees also dubbed Humphrey Bogart in his final film The Harder They Fall. Bogart was suffering at the time from what would be diagnosed as esophageal cancer and thus could barely be heard in some takes, hence the need for Frees to dub in his voice. He also voiced the cars in the comedy The Great Race.

Frees portrayed the Orson Welles sound-alike radio reporter in George Pal's film The War of the Worlds (1953), where he is seen dictating into a tape recorder as the military prepares the atomic bomb for use against the invading Martians. Memorably, his character says that the recording is being made "for Future history... if any". Frees also provided the film's dramatic opening narration, prior to Sir Cedric Hardwicke's voice-over tour of the solar system.

On rare occasions, Frees appeared on-camera, usually in minor roles. In 1954, he appeared in the film noir classic Suddenly starring Frank Sinatra and Sterling Hayden. He played a scientist in The Thing from Another World, a death-row priest in A Place in the Sun, and French fur trader McMasters in The Big Sky. In 1955, he appeared as an irate husband suing his wife (played by Ann Doran) for alimony in an episode of CBS's sitcom The Ray Milland Show.

At the MGM Animation studio, he also did multiple voice roles for the legendary Tex Avery's films, notably playing every role in Cellbound in 1955.

He had also done work for Hanna-Barbera in their Tom and Jerry shorts at MGM. In the 1956 Cinemascope Tom and Jerry cartoon, Blue Cat Blues, he was Jerry's voice who narrated the short; he had also voiced Jerry's cousin Muscles in Jerry's Cousin five years earlier and the cannibals in the Tom and Jerry episode His Mouse Friday where he said the lines "Mmmmm, barbecued cat!" and "Mmmmm, barbecued mouse!"

Frees narrated many live action films and television series, including Naked City (1958–1963). Paul Frees also provided the voice of the eccentric Billionaire John Beresford Tipton, always seated in his chair with his back to the viewer while talking to his employee Michael Anthony (fellow voice-artist Marvin Miller), on the dramatic series The Millionaire.

Frees also had a small live-action role for Disney in the 1959 film The Shaggy Dog, playing Dr. Galvin, a military Psychiatrist who attempts to understand why Mr. Daniels believes a Shaggy dog can uncover a spy ring. He also did the film's opening narration.

Although Frees was primarily known for his voice work (like Mel Blanc, he was known in the industry as "The Man of a Thousand Voices"), he was also a Songwriter and Screenwriter. His most notable screenwriting work was the little-seen 1960 film The Beatniks, a screed against the then-rising Beat counterculture in the vein of Reefer Madness. In 1992, the film was mocked on an episode of Mystery Science Theater 3000.

From October 1961 through September 1962, Paul Frees provided the voice for the shady Lawyer named Judge Oliver Wendell Clutch, a weasel on the animated program Calvin and the Colonel starring the voices of Freeman Gosden and Charles Correll, the series was an animated television remake of their radio series Amos 'n Andy.

For the 1962 Christmas special Mister Magoo's Christmas Carol, produced by UPA, Paul Frees voiced several characters, including Fezziwig, the Charity Man, two of the opportunists who steal from the dead man (Eyepatch Man and Tall Tophat Man) and Mister Magoo's Broadway theatre Director. He subsequently provided numerous voices for further cartoons in the series that followed, The Famous Adventures of Mr. Magoo.

Frees provided the voices of both John Lennon and George Harrison in the 1965 The Beatles cartoon series, the narrator, Big D and Fluid Man in the 1966 cartoon series, Frankenstein Jr. and The Impossibles and of The Thing in the 1967 series Fantastic Four, as well as President James Norcross in the 1967 cartoon series Super President. He played several roles—narrator, Chief of State, the judges and the bailiff—in the George Lucas / John Korty animated film, Twice Upon a Time.

He also provided voices for numerous characters at Disney parks, including the unseen "Ghost Host" in the Haunted Mansion attraction at Disneyland and Walt Disney World, and several audio-animatronic pirates, including the Auctioneer, in the Pirates of the Caribbean ride and recorded the iconic "Dead Men Tell No Tales" used in the ride. Disney eventually issued limited edition compact discs commemorating the two rides, featuring outtakes and unused audio tracks by Frees and others. Frees also provided narration for the Tomorrowland attraction Adventure Thru Inner Space (1967–1985) and the original Great Moments with Mr. Lincoln. Audio clips from the attractions in Frees' distinctive voice have even appeared in fireworks shows at Disneyland.

Since Frees' death, voice actor Corey Burton has provided voices for some of Frees's characters. Burton, who met Frees in the late 1970s, has re-recorded introductions for some Disneyland attractions that were originally recorded by Frees. In some cases, Frees' original, pre-digital recordings had simply deteriorated over time. Those that were slightly rewritten to reflect newer safety standards are performed by actors Joe Leahy (English) and Fabio Rodriguez (Spanish).

Frees provided the voice-over for the trailer to the 1971 Clint Eastwood thriller, Play Misty for Me.

Frees did the narration for the George Pal documentary The Fantasy Film Worlds of George Pal (1985), wriiten, produced, and directed by Arnold Leibovit. Two years later, Frees provided the voice for Arnie the Dinosaur and the Pillsbury Doughboy in The Puppetoon Movie (1987), also produced and directed by Leibovit.

Frees was professionally active until his death from heart failure on November 2, 1986. He was living in Tiburon, California, and was survived by his son and his daughter. His body was cremated and his ashes scattered over the Pacific Ocean.

A computer-animated singing bust in Frees' likeness appeared in the 2003 film The Haunted Mansion as a tribute. Similarly, audio recordings of Frees from the Pirates of the Caribbean attraction can be heard in Pirates of the Caribbean: At World's End in an homage to the ride.

For his contributions to the Disney legacy, Frees was honored posthumously as a Disney Legend on October 9, 2006.