While at Grand Ledge, Horford played AAU basketball for the Michigan Mustangs, who were runners-up in the Adidas Big Time National Tournament.

[4] There, he played for coach Billy Donovan and teamed up alongside Joakim Noah, Corey Brewer and Taurean Green.

[6] On April 2, 2007, the Gators repeated as national champions, becoming the first team to do so since the 1991–92 Duke Blue Devils, and the first ever to do so with the same starting lineup (Horford, Noah, Brewer, Green, and Lee Humphrey).

The Hawks finished the regular season with a 37–45 record and entered the playoffs as the eighth seed in the Eastern Conference.

In their first round match-up with the Boston Celtics, Horford helped the Hawks take the eventual champions to seven games, losing the series 4–3.

Horford contributed 14.2 points, 9.9 rebounds, 2.3 assists, 1.1 blocks and 0.7 steals in 35.1 minutes (.551 FG%, .789 FT%), appearing in 81 games.

[11] Playing alongside Mike Bibby, Jamal Crawford, Joe Johnson, Josh Smith and Marvin Williams, the Hawks entered the playoffs as the third seed in the East with a 53–29 record.

Horford appeared in the Hawks' first 11 games of the season before missing the final 55 due to a torn left pectoral muscle, an injury suffered on January 11, 2012, against the Indiana Pacers.

[30] In a brilliant stretch of play from December 7 to January 31, Horford scored in double digits in 28 consecutive games.

[31] Behind Horford and fellow All-Star teammates Paul Millsap, Kyle Korver and Jeff Teague, the Hawks finished the regular season with the best record in the East at 60–22, and advanced through to the Eastern Conference Finals for the first time since the 1960s, when the franchise was located in St.

[33] On December 4, Horford scored 16 points against the Los Angeles Lakers to extend his streak of double-digit games to 22, setting a career high.

[34][35] Horford's streak came to an end at 23 after scoring nine points against the Oklahoma City Thunder in the Hawks' 24th game of the season on December 10.

[39][40][41] Horford made his Celtics debut in their season-opening 122–117 victory over the Brooklyn Nets on October 26, 2016, recording 11 points, five rebounds, and six assists.

[43] He returned to action on November 19 and had 18 points, 11 rebounds, and five assists in a narrow 94–92 road victory over the Detroit Pistons.

[45] In Game 1 of the Celtics' second-round playoff series against the Washington Wizards, Horford nearly had a triple-double with 21 points, 10 rebounds, and nine assists during a 123–111 victory.

On November 12, 2017, Horford returned from a two-game absence with a concussion and scored 21 points on 8-of-9 shooting to help the Celtics hang on to narrowly beat the Toronto Raptors 95–94 for their 12th straight victory.

[49] On February 4, 2018, he made a 15-foot fadeaway jumper at the buzzer to lift the Celtics to a narrow 97–96 victory over the Portland Trail Blazers, finishing with 22 points, 10 rebounds, and five assists.

[55] On December 29, Horford scored 18 points with a career high-tying five three-pointers to go along with five rebounds and three assists in a 112–103 road victory over the Memphis Grizzlies.

[60] On October 23, 2019, Horford made his 76ers debut, recording 16 points, two rebounds, and three assists in a 107–93 victory over his former team, the Boston Celtics.

[61] On November 4, Horford scored a season-high 32 points, alongside five rebounds, four assists, and two steals in a 114–109 loss to the Phoenix Suns.

[62] The 76ers faced the Celtics during their first-round playoff series, but they were eliminated in a four-game sweep, with Horford only averaging 7.0 points per game.

[63] On December 8, 2020, Horford was traded, alongside a 2025 first-round pick and the draft rights to Théo Maledon and Vasilije Micić, to the Oklahoma City Thunder in exchange for Terrance Ferguson, Danny Green and Vincent Poirier.

[65] On February 5, 2021, Horford scored a season-high 26 points, alongside seven rebounds, eight assists, two steals, and three blocks in a 106–103 loss to the Minnesota Timberwolves.

[66] On March 27, the Thunder announced that Horford would sit out the rest of the season as the team prioritized developing its younger players.

[69] On May 7, 2022, in Game 3 of the Eastern Conference Semifinals, Horford scored 22 points to go along with 16 rebounds, five assists, two blocks, and no turnovers in a 103–101 loss against the reigning champion Milwaukee Bucks.

[74] In Game 1 of the Finals four days later, Horford led the Celtics to a 120–108 comeback victory over the Golden State Warriors with 26 points and six rebounds.

[78][79] On January 19, 2023, he had 20 points, 10 rebounds, and three blocks as he helped the Celtics beat the Golden State Warriors in overtime 121–118.

[81] With the arrival of offseason trade acquisition Kristaps Porziņģis, Horford would assume the role of a reserve, after having started nearly every game up to that point.

[82] On April 29, 2024, in Game 4 of the first round of the playoffs against the Miami Heat, Porziņģis was injured, putting Horford in line to be the Celtics' starting center.

[85] Ten days later, in Game 3 of the Eastern Conference Finals against the Indiana Pacers, Horford scored 23 points on a career-high seven three-pointers in a 114–111 comeback victory.