Reiner was born in the Bronx, New York City on March 20, 1922 to Irving and Bessie Reiner (née Mathias). His father was a watchmaker. His parents were Jewish immigrants; his father was from Austria and his mother Romania. His older brother Charles served in the 9th Division in World War II; his ashes are buried at Arlington National Cemetery.

Reiner was drafted into the United States Army Air Forces on October 27, 1942 and served during World War II, eventually achieving the rank of corporal by the end of the war. He initially trained to be a radio operator. After spending three months in the hospital recovering from pneumonia, he was sent to Georgetown University for ten months of training as a French interpreter. There he had his first experience as a director, putting on a Molière play entirely in French. After completing language training in 1944, he was sent to Hawaii to work as a teleprinter operator. The night before he was scheduled to ship out for an unknown assignment, he attended a production of Hamlet by the Special Services entertainment unit. Following an audition before actor and major Maurice Evans, he was transferred to Special Services. Over the following two years, Reiner performed around the Pacific theater, entertaining troops in Hawaii, Guam, Saipan, Tinian, and Iwo Jima until he was honorably discharged in 1946.

On December 24, 1943, Reiner married singer Estelle Lebost. The two were married for almost 65 years until her death in October 2008. Estelle delivered the iconic line “I’ll have what she’s having” in the deli scene of their son Rob’s 1989 film When Harry Met Sally…. They were the parents of Rob Reiner (b. 1947); poet, playwright, and author Annie Reiner (b. 1949); and painter, actor, and director Lucas Reiner (b. 1960). Reiner described himself as a Jewish atheist. He said, “I have a very different take on who God is. Man invented God because he needed him. God is us.” He said in 2013 he developed an atheistic viewpoint as the Holocaust progressed. Reiner was a Democrat. His residence was in Beverly Hills, California.

Reiner performed in several Broadway musicals (including Inside U.S.A. and Alive and Kicking) and had the lead role in Call Me Mister. In 1950, he was cast by Max Leibman as a comic actor on Sid Caesar’s Your Show of Shows, appearing on air in skits while also contributing ideas to writers such as Mel Brooks and Neil Simon. He did not receive credit for his sketch material, but won Emmy Awards in 1955 and 1956 as a supporting actor. Reiner also wrote for Caesar’s Hour with Brooks, Simon, Woody Allen, Larry Gelbart, Mel Tolkin, Mike Stewart, Aaron Ruben, Sheldon Keller, and Gary Belkin. He assumed the role of head writer and semi-regular on The Dinah Shore Chevy Show during the 1959-1960 television season.

In 1958, he wrote the initial 13 episodes of a television series titled Head of the Family, based on his own personal and professional life. However, the network disliked Reiner in the lead role for unknown reasons. In 1961, the series was recast and re-titled The Dick Van Dyke Show and became an iconic series, making stars of his lead actors Dick Van Dyke and Mary Tyler Moore. In addition to writing many of the episodes, Reiner occasionally appeared as show host Alan Brady. The series ran from 1961 to 1966 and thereafter entered a long run of syndication. In 1966, Reiner co-starred in The Russians Are Coming, the Russians Are Coming.

His first film directorial effort was an adaptation of Joseph Stein’s play Enter Laughing (1967), which, in turn, was based on Reiner’s semi-autobiographical 1958 novel of the same name. Balancing directing, producing, writing, and acting, Reiner worked on a wide range of films and television programs. Films from his early directing career include Where’s Poppa? (1970), Oh, God! (1977), and The Jerk (1979).

Starting in 1960, Reiner teamed with Brooks as a comedy duo on The Steve Allen Show. Their performances on television and stage included Reiner playing the straight man in 2000 Year Old Man. Eventually, the routine expanded into a series of five comedy albums and a 1975 animated television special, with the last album in the series winning a Grammy Award for Best Spoken Word Comedy Album. The act gave Brooks “an identity as a comic performer for the first time,” said Reiner. Brooks’s biographer William Holtzman called their 12-minute act “an ingenious jazz improvisation…” while Gerald Nachman described Reiner’s part in guiding the act:

From 1974 until 2001, he sponsored the Carl Reiner Charity Celebrity Tennis Tournament in La Costa, California, directed by international tennis player Mike Franks, which was played yearly over three days and included 400 players, of which 100 were professionals.

Reiner played a large role in the early career of Steve Martin by directing his first film The Jerk (1979) and directing and co-writing the comedian in Dead Men Don’t Wear Plaid (1982), The Man with Two Brains (1983), and All of Me (1984). Reiner also appeared in both The Jerk, playing a version of himself, and Dead Men Don’t Wear Plaid. In 1989, he directed Bert Rigby, You’re a Fool.

In 2000, he was honored with the Mark Twain Prize for American Humor at the Kennedy Center, where he was honored by fellow friends and comedians, Mel Brooks, Dick Van Dyke, Mary Tyler Moore, Steve Martin, Rob Reiner, Jerry Seinfeld, Ray Romano, and Joy Behar. A year later, he portrayed Saul Bloom in Ocean’s Eleven, Steven Soderbergh’s remake of 1960’s Ocean’s 11, and reprised his role in Ocean’s Twelve (2004) and Ocean’s Thirteen (2007). From 2004 to 2005, Reiner voiced Sarmoti in Father of the Pride. He claimed he knew how to play the role; in a teleconference, he said, “I spent my youth, from the time I was 6 to 18, living next to the Bronx Zoo. I knew the lions intimately. I watched them pace. They talked to me and I talked back to them. I learned that they have the worst breath of any animal in the world. I got my roar from the lions in person.” Reiner mentioned Siegfried & Roy, stating, “I think Siegfried immediately called Jeffrey [Katzenberg] and said it was very important to go forward with the show, to give the idea that Siegfried & Roy is continuing. Stopping the show would have stopped both of their performing lives. [Siegfried & Roy] were very excited about doing an animated show, and Siegfried thought the show was very helpful… because it helped [Roy] pull through a little faster. The two characters in the show are really funny and the show makes a very big deal of making them look silly. But, the sillier they are, the happier they are.” Based on his character of Sarmoti, Reiner stated that “curmudgeons always get the good lines.”

Reiner was the author of more than two dozen books. His first autobiographical novel, Enter Laughing (1958), led to a 1995 sequel, Continue Laughing. He published a memoir, My Anecdotal Life: A Memoir, in 2003. He also wrote a humorous series of memoirs under the titles I Remember Me (2012), I Just Remembered (2014), and What I Forgot To Remember (2015), along with books about film and art. He began to write children’s books based on the stories he used to tell a certain grandchild who would request, “Tell me a scary story, Grandpa, but not too scary.”

In 2012, he appeared as a guest on Jerry Seinfeld’s show Comedians in Cars Getting Coffee. They talked at a diner about his comedy career and Reiner invited Jerry to come and have dinner with Mel Brooks and himself. Reiner reported that every night, Brooks headed to his house to eat, watch Jeopardy (he taped it), and watch movies. He went on to offer the one rule for movies was that it had to be one where “somebody says, ‘Secure the perimeter!’ or ‘Get some rest.'” Brooks “falls asleep with his mouth open” every time. He briefly rapped under the alias “Gnarly Carly” on The Queen Latifah Show.

Reiner joined Twitter in 2012, tweeting that he was doing so to keep up with his grandson Jake. He felt obliged to post at least once per day, and so posted 6,520 tweets and accumulated 367,000 followers. His favorite topics were movies and Donald Trump, but his final tweet was a reminiscence about Noël Coward performing in Las Vegas. At the age of 98, Reiner was the oldest celebrity to actively use Twitter.

On October 31, 2018, Reiner, then 96, publicly denounced Donald Trump’s administration, and stated his goal –which he would not achieve– to live past November 3, 2020 and see Trump voted out of office.

Reiner appeared in dozens of television specials from 1967 to 2000. He also guest starred in several television series from the 1950s until his death in 2020. In May 2009, he guest starred as a clinic patient in “Both Sides Now,” the season five finale of House. He also voiced Santa in Merry Madagascar (2009) and reprised his role in the 2010 Penguins of Madagascar episode “The All Nighter Before Christmas.” In season 7 (December 2009) of Two and a Half Men, he guest-starred as television producer Marty Pepper. In 2010, he guest starred in three of the first-season episodes of Hot in Cleveland as Elka Ostrovsky’s (Betty White) date and reprised his role in February 2011. He also made appearances in The Cleveland Show as Murray and wrote the story for the episode “Your Show of Shows”, named after the program that started his career. Reiner reprised his role on Two and a Half Men in seasons 8 (October 2013) and 11 (January 2014).

On June 29, 2020, Reiner died at his home in Beverly Hills, California in the company of his family. He was 98 years old. According to his nephew, George Shapiro, Reiner fell while leaving his TV room at around 10:00 p.m. Pacific Time and lost consciousness. His cause of death was officially confirmed to be natural causes.