Carter was born in Culver City, California in 1954 to Jim Carter, an aircraft worker, and his wife, Inge. Gary was athletic at a young age, winning (along with four other boys) the 7-year old category of the first national Punt, Pass, and Kick skills competition in 1961. When Gary was 12, his mother died of leukemia. He attended high school at Sunny Hills High School, in Fullerton, California, where he played football as a quarterback and baseball as an infielder. After receiving more than 100 scholarships for athletics, Carter signed a letter of intent to play football for the UCLA Bruins as a quarterback, but instead signed with the Montreal Expos after they drafted him in the 1972 Major League Baseball Draft.

The Expos converted Carter to a catcher in the minor leagues. In 1974, he hit 23 home runs and drove in 83 runs for the Expos’ triple-A affiliate, the Memphis Blues. Following a September call-up, Carter made his major league debut in Jarry Park in Montreal in the second game of a double header against the New York Mets on September 16. Despite going 0–4 in that game, he finished the season batting .407 (11-27). He hit his first major league home run on September 28 against Steve Carlton in a 3–1 victory over the Philadelphia Phillies.

Carter split time between right field and catching during his rookie season (1975), and was selected for the National League All-Star team as a right fielder. He did not get an at bat, but appeared as a defensive replacement for Pete Rose in the ninth inning, and caught Rod Carew’s fly ball for the final out of the NL’s 6–3 victory. In that rookie season, Carter hit .270 with 17 home runs and 68 runs batted in, receiving The Sporting News Rookie of the Year Award and finishing second to San Francisco Giants pitcher John Montefusco for the National League Rookie of the Year award. That year, he was voted the Expos Player of the Year for the first of four times (he also won in 1977, 1980 and 1984).

Carter again split time in the outfield and behind the plate in 1976 while a broken finger limited him to 91 games. He batted .219 with six home runs and 38 RBIs. In 1977, young stars Warren Cromartie, Ellis Valentine and Andre Dawson became full-time outfielders. By June, starting catcher Barry Foote was traded, opening up a regular starting position for Carter behind the plate. He responded with 31 home runs and 84 RBIs. In 1980, Carter clubbed 29 home runs, drove in 101 runs, and earned the first of his three consecutive Gold Glove Awards. He finished second to third baseman Mike Schmidt in NL MVP balloting, whose Phillies took the National League East by one game over the Expos.  Carter caught Charlie Lea’s no-hitter on May 10, 1981, during the first half of the strike shortened season. The season resumed on Sunday, August 9, 1981 with the All-Star Game. Carter was elected to start his first All Star Game over perennial NL starting catcher Johnny Bench who had moved to play first base that year, and responded with two home runs and being named the game’s MVP. Carter was the fifth and most recent player to hit two home runs in an All-Star Game.

MLB split the 1981 season into two-halves, with the first-place teams from each half in each division meeting in a best-of-five divisional playoff series. The four survivors moved on to two best-of-five League Championship Series. The Expos won the NL East’s second half with a 30–23 record. In his first post season, Carter batted .421, hit two home runs and drove in six in the Expos’ three games to two victory over the Phillies in the division series. Carter’s average improved to .438 in the 1981 National League Championship Series, with no home runs or RBIs, and his Expos lost to the Los Angeles Dodgers in five games.  Pierre Elliott Trudeau, then prime minister of Canada, once remarked of Carter’s popularity saying “I am certainly happy that I don’t have to run for election against Gary Carter.” However some Expos were put off by Carter’s unabashed enthusiasm, feeling that he was too taken with his image and basked in his press coverage too eagerly, derisively naming him “Camera Carter”. Andre Dawson “felt [Carter] was more a glory hound than a team player”.

In his first game as a Met on April 9, 1985, he hit a tenth-inning home run off Neil Allen to give the Mets a 6–5 Opening Day victory over the St. Louis Cardinals. The Mets and Cardinals rivaled for the National League East championship, with Carter and first baseman Keith Hernandez leading the Mets. The season came down to the wire as the Mets won 98 games that season; however, they lost the division to a Cardinals team that won 101 games. Carter hit a career high 32 home runs and drove in 100 runs his first season in New York. The Mets had three players finish in the top ten in NL MVP balloting that season (Dwight Gooden 4th, Carter 6th and Hernandez 8th).

A rivalry also developed between the Mets and Carter’s former team, the Expos. On July 30 while facing the Expos at Shea, Montreal pitcher Bill Gullickson threw a pitch over Carter’s head. Gooden did the same to Gullickson in the bottom of the inning. The Los Angeles Times speculated that Carter caught the ball as if he knew where the pitch was going to end up.

In 1986, the Mets won 108 games and took the National League East by 211⁄2 games over the Phillies. Carter suffered a postseason slump in the NLCS, batting .148. However, he hit a walk-off RBI single to win Game 5. Carter also had two hits in Game 6 which the Mets won in 16 innings.  The Mets won the 1986 World Series in seven games over the Boston Red Sox. Carter batted .276 with nine RBIs in his first World Series, and hit two home runs over Fenway Park’s Green Monster in Game Four. He is the only player to hit two home runs in both an All-Star Game (1981) and a World Series game. Carter started a two-out rally in the tenth inning of Game 6, scoring the first of three Mets runs that inning on a single by Ray Knight. He also hit an eighth-inning sacrifice fly that tied the game. Carter finished third on the NL MVP ballot in 1986.

Carter batted .235 in 1987, and ended the season with 291 career home runs. He had 299 home runs by May 16 1988 after a fast start, then slumped until August 11 against the Chicago Cubs at Wrigley Field when he hit his 300th. During his home run drought, Carter was named co-captain of the team with Hernandez, who had been named captain the previous season.  Carter ended 1988 with 11 home runs and 46 RBIs—his lowest totals since 1976. He ended the season with 10,360 career putouts as a catcher, breaking Detroit Tigers catcher Bill Freehan’s career mark (9941). The Mets won 100 games that season, taking the NL East by fifteen games. However, the heavily favored Mets lost to the Los Angeles Dodgers in the 1988 National League Championship Series. Carter batted .183 in fifty games for the Mets in 1989. In November the Mets released Carter after five seasons, hitting 89 home runs and driving in 349 runs.

After leaving the Mets, Carter platooned with catcher Terry Kennedy on the San Francisco Giants in 1990, batting .254 with nine home runs. He found himself again in a pennant race in 1991 with the Los Angeles Dodgers, who finished one game behind the Atlanta Braves in the National League West.  At the end of the season, Carter returned to Montreal for his final season off waivers from the Dodgers. Carter was still nicknamed “Kid” by teammates despite his age. In his last at-bat, he hit a double over the head of Chicago Cub right-fielder Andre Dawson, the only other player to go into the Hall of Fame as an Expo. The Expos went 87-75 and finished second behind the Pittsburgh Pirates in the National League East.

Carter was inducted into the New York Mets Hall of Fame in 2001. In 2003, Carter was elected into the Canadian Baseball Hall of Fame along with Kirk McCaskill, and his number eight was retired by the Expos and is tacitly recognized on the facade of Nationals Park in Washington, D.C..

In his sixth year on the ballot, Gary Carter was elected to the Baseball Hall of Fame along with Eddie Murray on January 7, 2003. Carter had originally expressed a preference during his final season to be inducted as an Expo. Given the uncertainty of the Expo franchise, Carter’s employment by the Mets organization since retiring as a player, his World Series title with the Mets, and his media celebrity during his stint in New York, following his election Carter shifted his preference to be enshrined with a Mets cap. The New York City media strongly supported Carter’s preference to go into the Hall as a Met. Carter “joked that he wanted his Cooperstown cap to be a half-and-halfer, split between the Expos and Mets”. The final decision rested with the Hall of Fame, and Hall president Dale Petroskey declared that Carter’s achievements with the Expos over twelve season had earned his induction, whereas his five seasons with the Mets by itself would not have, saying “we want to have represented on the plaque the team that best represents where a player made the biggest impact in his career. When you look at it, it’s very clear. Gary Carter is an important part of the history of the Expos”. Carter was the first Hall of Famer whose plaque depicts him with an Expos logo. At the induction ceremony, Carter spoke a few words of French, thanking fans in Montreal for the great honor and pleasure of playing in that city, while also taking great care to note the Mets’ 1986 championship as the highlight of his career.

After the Expos moved to Washington, D.C. to become the Washington Nationals following the 2004 season, a banner displaying Carter’s number along with those of Andre Dawson, Tim Raines and Rusty Staub was hung from the rafters at the Bell Centre, home of the NHL’s Montreal Canadiens. While the Mets have not retired number eight, it has remained unused since Carter’s election to the Hall of Fame.

Carter was named Gulf Coast League Manager of the Year his first season managing the Gulf Coast Mets in 2005. A year later, he was promoted to the A-level St. Lucie Mets, and guided his team to the 2006 Florida State League championship, again earning Manager of the Year honors. In recent years, Carter has been criticized, most notably by former co-captain Keith Hernandez, for twice openly campaigning for the Mets’ managerial position while it was still occupied by incumbents Art Howe in 2004, and in 2008 Willie Randolph.

In 2008, he managed the Orange County Flyers of the Golden Baseball League, and again guided his team to the GBL Championship and was named Manager of the Year. For the following season Carter was named manager of the Long Island Ducks of the independent Atlantic League of Professional Baseball. The Ducks won the 2009 second half Liberty Division title, but they were defeated by the Southern Maryland Blue Crabs in the Liberty Division playoffs. The next season Carter was named head baseball coach for the NCAA Division II Palm Beach Atlantic University Sailfish.

He and his wife, Sandy, were married in 1975. They had three children.  His daughter Kimmy is the head softball coach at Palm Beach Atlantic and was a softball catcher for Florida State from 1999-2002.  Carter was an active philanthropist. Through The Gary Carter Foundation, of which Carter was the president, Carter and his staff support 8 Title I schools in Palm Beach County whose students live in poverty. Typically, these schools have 90% or more students eligible for free or reduced lunches. The Foundation seeks to “better the physical, mental and spiritual well being of children.” To accomplish this, they advocate “school literacy by encouraging use of the Reading Counts Program, a program that exists in the Palm Beach County School District”. Since its inception, The Gary Carter Foundation has placed over $622,000 toward charitable purposes, including $366,000 to local elementary schools for their reading programs.

In May 2011, Carter was diagnosed with four malignant tumors in his brain after experiencing headaches and forgetfulness. Doctors confirmed that he had a grade IV primary brain tumor known as glioblastoma multiforme. Doctors said that the extremely aggressive cancer was inoperable and Carter would undergo other treatment methods to shrink his tumor. On January 20, 2012, daughter Kimmy posted on her blog that an MRI had revealed additional tumors on her father’s brain. Even as he battled an aggressive form of brain cancer, Carter did not miss Opening Day for the college baseball team he coached.

Carter died of brain cancer on February 16, 2012. He was 57 years old. On February 25, 2012, the Mets announced that they were adding a memorial patch to their uniforms in Carter’s honor for the entire 2012 season. The patch features a black home plate with the number 8 and “KID” inscribed on it. On the Mets’ 2012 opening day, the Carter family unveiled a banner with a similar design on the center field wall of Citi Field.

The NHL’s Montreal Canadiens, who had purchased the mascot and hung retired numbers in its arena after the Expos relocation to Washington, paid tribute to Gary Carter by presenting a video montage and observing a moment of silence before a game against the New Jersey Devils on February 20, 2012. All Canadiens players took to the ice during pre-game warm-ups wearing number 8 Carter jerseys, and Youppi! appeared wearing an Expos uniform. In addition, Youppi! wore a patch on his Canadiens jersey featuring a white circle with a blue number 8 inside it for the remainder of the season.

Tom Verducci, longtime Sports Illustrated baseball writer, reminisced about Carter following his death, “I cannot conjure a single image of Gary Carter with anything but a smile on his face. I have no recollection of a gloomy Carter, not even as his knees began to announce a slow surrender … Carter played every day with the joy as if it were the opening day of Little League.” “Gary actually took a lot of grief from his teammates for being a straight arrow. It wasn’t the cool thing to do but on the same token, I think he actually served as a role model for a lot of these guys as they aged. He was the ballast of that team. They did have a lot of fun, there’s no question about that, but they were also one of the fiercest, most competitive teams I’ve ever seen and obviously their comebacks from the ’86 postseason defines that team. Carter was a huge part of that.”

Faillon Street W. in Montreal, near the former Jarry Park stadium, has been renamed Gary-Carter Street in his honour.  On March 28, 2014, during an exhibition game between the Toronto Blue Jays and the New York Mets at Olympic Stadium in Montreal, QC, a banner was unveiled in honour of Gary Carter in a special ceremony before the first pitch. Carter’s widow Sandy and daughter Kimmy were present on field for an emotional video tribute and the unveiling of the banner on the outfield wall, which reads “Merci! Thank You!” and contains an image of a baseball overlaid with Carter’s retired number 8.