Garrett was born Bradley Harold Gerstenfeld in Woodland Hills, California, the son of Barbara (née Colton), a homemaker, and Al Gerstenfeld, a hearing aid salesman. He has two older brothers, Jeff and Paul. He attended George Ellery Hale Middle School in Woodland Hills, California and graduated from El Camino Real High School in Woodland Hills. He attended UCLA for less than two months before dropping out to pursue his comedy career.
Garrett started out at various improv clubs in Los Angeles, including The Improv in Hollywood and The Ice House in Pasadena. In 1984, he became the first $100,000 grand champion winner in the comedy category of the TV show Star Search. This led to his first appearance, at age 23, on The Tonight Show starring Johnny Carson, making him one of the youngest comedians ever to perform on the show. His appearance with Carson brought Garrett a lot of national attention, and soon he was appearing as an opening act for such headliners as Diana Ross and Liza Minnelli. He also opened in Las Vegas for Frank Sinatra, David Copperfield, Smokey Robinson, Sammy Davis, Jr., the Beach Boys, the Righteous Brothers and Julio Iglesias.
After achieving a strong measure of success with stand-up comedy, Garrett decided to change gears and try his luck with performing on TV. He was the voice of wrestling legend Hulk Hogan for the cartoon series Hulk Hogan's Rock 'n Wrestling, He was featured on Family Feud during Ray Combs's tenure in a "Funny Men vs. Funny Women Week" during November sweeps. He also appeared for a week on the game show Super Password in 1987. He then appeared in the short-lived summer comedy First Impressions (CBS, 1988), in which he was a divorced father who makes a living doing impressions, in a one-time spot as a bank loan officer on Roseanne (ABC), and The Pursuit of Happiness (NBC, 1995-96), in which he was the hero's gay best friend. Though prior to these roles, Garrett had also had a minor part on Transformers, voicing the Decepticon base Trypticon in season three and as an ill-fated thug in Suicide Kings. He soon won the role of Ray Romano's brother Robert Barone on the long-running sophisticated but family-oriented comedy hit Everybody Loves Raymond. Garrett has also made an appearance on The Fresh Prince of Bel-Air and played a hitman who tried to kill Will Smith.
Garrett's distinctive deep voice has landed him notable work as a voice actor, such as on the animated series the Mighty Ducks: The Animated Series, 2 Stupid Dogs, Project Geeker, A Bug's Life, Asterix and the Vikings, Justice League Unlimited, Finding Nemo, and as Auguste Gusteau in Pixar's Ratatouille. His role on Everybody Loves Raymond won him five Emmy nominations, and the 2002, 2003 and 2005 Emmy Awards for Best Supporting Actor in a Comedy.
In 1990, Garrett appeared as a semi-regular panelist on the revival of Match Game. On the May 2, 1996 episode of the sitcom Seinfeld, called "The Bottle Deposit", Garrett played a deranged auto mechanic who steals Jerry Seinfeld's car.
In 2003, he was also nominated for the Emmy for Outstanding Lead Actor in a Miniseries or a Movie for Gleason. With his Raymond castmates, he won the 2003 Screen Actors Guild Award for Outstanding Performance by an Ensemble in a Comedy Series. He won the fifth season championship of Celebrity Poker Showdown, and played in the 2005, 2006 and 2007 World Series of Poker. Garrett was hoping to do a spinoff with his character Robert Barone from Everybody Loves Raymond when the show ended its nine-year run on TV in 2005, but he withdrew in October 2005 due to inaction from CBS that led to a number of the writers from "Raymond" leaving and taking other jobs.
In 2005, Garrett appeared on Broadway playing Murray the Cop in the revival of Neil Simon's The Odd Couple with Nathan Lane and Matthew Broderick. He understudied Lane in the role of Oscar Madison, and substituted for him in January, 2006, during Mr. Lane's illness. In 2006, Fox network announced they would pick up a new sitcom called 'Til Death starring Brad Garrett in