He graduated from Notre Dame High School in Sherman Oaks, Los Angeles, before the Marlins selected him in the second round of the 2007 MLB draft.

[18] He won numerous post-season awards for his performance in the 2008 minor league season, and was placed at number 16 on Baseball America's top 100 prospects list.

[19] Stanton began the 2009 season with the Jupiter Hammerheads of the Class A-Advanced Florida State League, where he batted .294 with 12 home runs and 39 RBIs.

On May 6, 2010, Stanton hit a home run against the Montgomery Biscuits that cleared the scoreboard in center field and traveled an estimated 500 to 550 feet (150 to 170 m).

He joined Jeff Conine, Chuck Carr, Quilvio Veras, Craig Counsell and Jeremy Hermida on the list of Marlins whose first homer came with the bases loaded.

In addition, Stanton became the fourth player in the past 25 years to hit his first career grand slam before his 21st birthday along with Jose Reyes (2003), Andruw Jones (1997) and Alex Rodriguez (1996).

[38] On May 21, 2012, Stanton hit a grand slam off Jamie Moyer that traveled 462 feet (141 m) with an exit velocity of 122.4 miles per hour (197.0 km/h), the fastest since ESPN's Home Run Tracker[39] began tracking.

After having a career-best .290 batting average, 37 home runs, and a .608 slugging percentage, Stanton had a good feeling coming into the 2013 season from spring training and participating in the WBC team USA.

With only 116 games played he was not able to put up equivalent numbers: for 425 at-bats he had a .249 average with 106 hits, 62 RBIs, and 24 home runs by season's end.

On the last day of the regular season against the Detroit Tigers, Stanton scored the winning run on a wild pitch to complete Henderson Álvarez's no-hitter.

On September 11, Stanton was hit by a pitch in the face by Milwaukee Brewers pitcher Mike Fiers, and was at first expected to resume play, but subsequent examination determined the injury was more serious.

[52][53] At the time of his season-ending hand injury in June, Stanton had played only 74 games but hit 27 home runs, with a batting average of .265.

[62] On April 12, 2017, Stanton hit two home runs, the second one landing in a pool behind the left-center field, prompting a fan to dive in to retrieve the ball.

[67] Named NL Player of the Week on August 13, Stanton had hit his 250th career home run earlier in the day versus the Colorado Rockies.

Stanton hit the home run versus Ty Blach and had homered in five consecutive games, setting another franchise record.

[74] Enhancing the cachet of Stanton's historic season, ESPN ranked Marlins Park as one of the six most difficult stadiums in which to hit a home run in 2017.

[77] Before Game 2 of the World Series, Stanton was presented with the Hank Aaron Award, the second of his career, as the "most outstanding offensive performer" in the National League.

On November 16, Stanton was named the National League's Most Valuable Player, beating out Cincinnati Reds' first baseman Joey Votto by two voting points.

[78] At the end of his MVP season, Stanton was the holder of 10 Marlins records including most career home runs (267), RBIs (672), slugging percentage (.554), total bases (1,983), strikeouts (1,140), and single-season records for home runs (59), RBIs (132), slugging percentage (.631), extra-base hits (91), and total bases (377).

[79] On December 11, 2017, the New York Yankees acquired Stanton and cash considerations from the Marlins for Starlin Castro and minor leaguers Jorge Guzmán and José Devers.

For the fourth consecutive year, he hit the ball with the highest exit velocity of the season in the major leagues, which was 121.7 miles per hour.

In the 2018 AL Wild Card Game against the Oakland Athletics, Stanton hit his first career postseason home run off of Blake Treinen.

[92] In Game 1 of the 2020 American League Division Series on October 5, Stanton hit a grand slam in the ninth inning to propel the Yankees to a 9–3 win over the Tampa Bay Rays.

Stanton went 3-for-4 with a home run and two long singles that hit off the top of the Green Monster in the Yankees' 6–2 loss to the Red Sox in the American League Wild Card Game.

On June 17, Stanton hit his 361st home run during a game against the Toronto Blue Jays, tying Joe DiMaggio's career record as the 84th player on the all-time list.

[104] On October 18, Stanton hit a three-run home run in the deciding Game 5 of the ALDS against the Cleveland Guardians, helping propel the Yankees to the ALCS.

[105] During a game against the Colorado Rockies on July 15, Stanton recorded his 1,000th RBI, going 1-for-3 with a three-run home run off Connor Seabold and 4 RBIs.

[106] On September 5, Stanton hit his 400th career home run (a 451-foot, two-run blast) during a game against the Detroit Tigers off pitcher José Cisnero.

[113][114] In the ALCS against the Cleveland Guardians, Stanton hit four home runs and had an OPS of 1.222 in five games, winning the LCS MVP Award as the Yankees advanced to the 2024 World Series.

After a trip to Europe in the 2011–12 offseason (during which he frequently heard names like Gianpiero, Gianpaolo, and Gianluigi) he made it known before the 2012 season that he preferred to be called Giancarlo.