Berg was born Tilly Edelstein in 1898 in Harlem to Jacob and Diana Edelstein, natives of Russia and England, respectively. Tilly attended public schools. She married Lewis Berg in 1918; they had two children, Cherney (1922–2003) and Harriet (1926–2003). She learned theater while producing skits at her father's Catskills Mountains resort in Fleischmanns, New York.
After the sugar factory her husband worked at burned down, she developed a semi-autobiographical skit, portraying a Jewish family in the New York tenements, into a radio show. Though the household had a typewriter, Berg wrote her script by hand, taking the pages this way to a long-awaited appointment at NBC. When the executive she was meeting with protested that he could not read what Berg had written, she read the script aloud to him. Her performance not only sold the idea for the radio program but also got Berg the job as the lead actress on the program she had written. Berg continued to write the show's scripts by hand in pencil for as long as the program was on the air. On November 20, 1929, a 15-minute episode of The Rise of the Goldbergs was first broadcast on the NBC radio network. She started at $75 a week. Less than two years later, in the heart of the Great Depression, she let the sponsor propose a salary and was told, "Mrs. Berg, we can't pay a cent over $2,000 a week." Berg's husband, Lewis, who became a successful consulting engineer after the loss of his job which prompted her to write the initial radio script, refused to be photographed with his wife for publicity purposes, as he felt this was infringing on her success.
Berg became inextricably identified as Molly Goldberg, the bighearted matriarch of her fictitious New York family who moved to Connecticut as a symbol of Jewish-American upward mobility. She wrote practically all the show's radio episodes (more than 5000) plus a Broadway adaptation, Me and Molly (1948). It took considerable convincing, but Berg finally prevailed upon CBS to let her bring The Goldbergs to television in 1949. Early episodes portrayed the Goldberg family openly and personally struggling to adapt to American life. Just as Berg started in her autobiography, she chose to depict her Jewish grandfather's worship to America and the new world in her first radio broadcast show. Her characters Molly, Jake, Sammy and Rosie emphasized her day to day stories of Jewish immigration to America.
Immigrant life and the Goldberg family struggle were familiar and relatable to most families during this point in American history. Radio seemed to lend a hand to new settlers and produced a common place to tie patriotism and families together. The program's victory is largely because of the familiar feelings of the American people portrayed in the program's scripts. The first season script was later published into a book form.
Berg won the first ever Emmy Award for Lead Actress in a Comedy Series her debut year on the network—her twentieth consecutive year of playing the role—and the show stayed in production for five years.
The Goldbergs ran into trouble in 1951, during the McCarthy Era. Co-star Philip Loeb (Molly's husband, patriarch Jake Goldberg) was one of the performers named in Red Channels: The Report of Communist Influence in Radio and Television and blacklisted as a result. Loeb resigned rather than cause Berg trouble. He reportedly received a generous severance package from the show, but it didn't prevent him from sinking into the depression that ultimately drove him to suicide in 1955. The Goldbergs returned a year after Loeb departed the show and continued until 1954, after which Berg also wrote and produced a syndicated film version. The show remained in syndicated reruns for another few years, after one year of production and 39 episodes (it aired on some stations as Molly).
In 1959, Berg won the Tony Award for Best Actress for her performance in A Majority of One. She made guest appearances on The Martha Raye Show and The Pat Boone Chevy Showroom. On February 6, 1958, she appeared on NBC's The Ford Show, Starring Tennessee Ernie Ford. In 1961, Berg won the Sarah Siddons Award for her work in Chicago theatre. Berg also published a best-selling memoir, Molly and Me, in 1961. That same year, she made a last stab at television success in the Four Star Television situation comedy, Mrs. G. Goes to College (retitled The Gertrude Berg Show at midseason). Her costars were Cedric Hardwicke, Mary Wickes and Marion Ross. Berg played a 62-year-old widow who decides to attend college. She was also the mystery guest on the series, What's My Line 3 different times circa early 1960s.
Berg was also a songwriter. Her composition, "That Wonderful Someone", even found its way into the repertoire of country music singer Patsy Cline, appearing on Cline's 1957 debut album.
A biography of Berg, Something on My Own: Gertrude Berg and American Broadcasting, 1929–1956, by Glenn D. Smith, Jr. (Syracuse University Press) appeared in 2007. Aviva Kempner's 2009 documentary, Yoo-Hoo, Mrs. Goldberg, deals with Berg's career, and to an extent, her personal life.
Berg died of heart failure on September 14, 1966, aged 67, in a Manhattan hospital. She is buried in Clovesville Cemetery. Her husband, Lewis, died in 1985, aged 87.