He was born on April 15, 1917 in Baltimore, Maryland to Hans Georg and Edith Beryl (née Gildersleeve) Conried. He was named Hans Georg Conried Jr. Claims that his real name was Frank Foster are false. His Connecticut-born mother was a descendant of Pilgrims, and his father was a Jewish immigrant from Vienna, Austria. He was raised in Baltimore and in New York City.
He studied acting at Columbia University and went on to play major classical roles onstage. Conried worked in radio before working in movies in 1939. During World War II, he enlisted in the United States Army in September 1944.
One of Conried's early radio appearances came in 1937, when he appeared in a supporting role in a broadcast of The Taming of the Shrew on KECA in Los Angeles, California. Four years later, a newspaper reported about his role on Hedda Hopper's Hollywood: "But at the mike he's equally convincing as old men, drunks, dialeticians, or Shakesperean tragedians. Miss Hopper favors him for her dramatizations when the script will allow him, as she puts it, 'to have his head.'"
Conried appeared regularly on radio during the 1940s and 1950s. He was in the regular cast of Orson Welles's Ceiling Unlimited, for which he wrote the December 14, 1942, episode, "War Workers". On CBS's The George Burns and Gracie Allen Show he played a psychiatrist whom George regularly consulted for help in dealing with the ditzy Gracie.
Conried made his Broadway debut in Can-Can and was credited in six films (among them The Twonky and The 5,000 Fingers of Dr. T), all in 1953. Other Broadway productions include 70, Girls, 70 and Irene. He can be clearly heard on the Original Cast Albums (and CDs) of Cole Porter's "Can-Can" and Kander & Ebb's "70, Girls, 70" where, among other songs, Conried performs a sensational fast-paced patter song called "The Caper."
Conried's inimitable growl and impeccable diction were well suited to the roles he played, whether portraying the dim Professor Kropotkin in the radio show My Friend Irma or portraying comic villains and mock-sinister or cranky types, such as Walt Disney's Mr. Darling, and Captain Hook in Peter Pan (1953), and The Grinch/Narrator from Dr. Seuss' Halloween is Grinch Night. According to the DVD commentary of Futurama, he was the inspiration for the voice created for that series' "Robot Devil".
Conried was a cast member of other Dr. Seuss specials, and The Rocky and Bullwinkle Show, voicing the character of Snidely Whiplash in the Dudley Do-Right shorts, and hosted Fractured Flickers, another creation of Jay Ward and Bill Scott, as well as Wally Walrus on The Woody Woodpecker Show, Uncle Waldo P. Wigglesworth on Hoppity Hooper, and Dr. Dred on Drak Pack. He also performed as the "slave in the mirror" character, hosting several memorable episodes of Walt Disney's Wonderful World of Color.
Besides hosting Fractured Flickers, Conried was a regular panelist on CBS's pantomime program, Stump the Stars and a semi-regular guest on the Ernie Kovacs-hosted game show Take a Good Look. He was a regular guest on Jack Paar's Tonight Show on NBC from 1959 to 1962. Conried joined the cast of The Tony Randall Show during the 1977-78 season.
Guest appearances included I Love Lucy (as the English tutor Percy Livermore) Davy Crockett, The Californians, Meet McGraw, Hey, Jeannie!, The Ray Milland Show, The DuPont Show with June Allyson, The Real McCoys, The Many Loves of Dobie Gillis, Mister Ed, The Islanders, Ben Casey, Dr. Kildare, Lost in Space, Daniel Boone, The Beverly Hillbillies, The Lucy Show, Gilligan's Island, The Monkees, Have Gun – Will Travel, Love, American Style, Here's Lucy, Kolchak, Alice, Laverne & Shirley, The Love Boat, Hogan's Heroes, Match Game, Maverick, The Donna Reed Show, What's It For, Fantasy Island and Quark.
From 1955-64, Conried made twenty-one guest appearances as Danny Thomas's Lebanese "Uncle Tonoose" in Make Room for Daddy on ABC and then CBS. He was featured in the 1958 episode "What Makes Opera Grand?" on the anthology series Omnibus. The episode, an analysis by Leonard Bernstein showing the powerful effect of music in opera, featured Conried as Marcello in a spoken dramatization of Act III of Puccini's La Bohème. The program demonstrated the effect of the music in La Bohème by having actors speak portions of the libretto in English, followed by opera singers singing the same lines in the original Italian.
He married Margaret Grant on January 29, 1942; the couple had four children. He had a history of heart problems and suffered a stroke in 1974. He managed to remain active until his death on January 5, 1982, one day after suffering a massive heart attack.