- June 23, 2016: Drafted by the Philadelphia 76ers in the 1st round (1st pick) of the 2016 NBA Draft.
- July 2, 2016: Signed a multi-year contract with the Philadelphia 76ers.
- July 16, 2019: Signed a multi-year contract with the Philadelphia 76ers. (Signing is extension on deal signed in 2016.)
- February 10, 2022: Traded by the Philadelphia 76ers with Seth Curry, Andre Drummond, a 2023 1st round draft pick (Brice Sensabaugh was later selected) and a 2027 1st round draft pick ( was later selected) to the Brooklyn Nets for James Harden and Paul Millsap. Philadelphia also received a trade exception 2023 1st-rd pick was originally a 2022 pick that was deferred 2027 1st-rd pick is top-8 protected and could turn into cash in 2029

COLLEGE

Simmons made his debut for LSU on 15 August in a 89–75 win over the Newcastle All-Stars in the first game of LSU's preseason Australia trip. His double-double of 22 points and 10 rebounds led the way for the Tigers, playing at the Newcastle Basketball Stadium where his father played professionally for the Newcastle Falcons in the late 1990s.

On 13 November 2015, Simmons made his college debut in LSU's season opener, recording a double-double with 11 points and 13 rebounds as a starter in a win over McNeese State.[50] He helped LSU start the season 3–0 before recording 21 points, 20 rebounds, 7 assists and 2 steals in a loss to Marquette on 23 November.] On 2 December, he helped LSU break a three-game losing streak by recording 43 points, 14 rebounds, 7 assists, 5 steals and 3 blocks in a 119–108 win over North Florida. His 43 points were the most for a Tigers player since Shaquille O'Neal had 43 against Northern Arizona on 28 December 1991. After recording 14 points and 10 rebounds in a win over Kentucky on 5 January 2016, Simmons was dubbed the best all-around player since LeBron James by NBA Hall of Famer Magic Johnson. On 11 February, he was named to the 35-man midseason watchlist for the Naismith Trophy. Nine days later, Simmons came off the bench for the first time after being removed from LSU's starting lineup for their game against Tennessee due to academic reasons. Following the conclusion of the regular season, Simmons was named first-team All-Southeastern Conference and the League Freshman of the Year on the 2016 Coaches SEC voting. He was also named to the eight-player All-SEC Freshman team. LSU finished the regular season with a 18–13 record, including 11–7 in SEC play.

As the fourth seed in the 2016 SEC Tournament, Simmons helped LSU (18–13) defeat Tennessee in the Quarterfinalsto move on to the semi finals where they faced first-seeded Texas A&M. LSU bowed out of the tournament with a demoralising 71–38 loss to the Aggies, as Simmons was unsuccessful in leading the Tigers to a NCAA tournament berth. Simmons completed the 2015/16 season having played in 33 games with 32 starts. He led the team in all major statistical categories except three-point and free throw shooting, finishing with averages of 19.2 points, 11.8 rebounds, 4.8 assists, 2.0 steals and 0.8 blocks in 34.9 minutes per game, while shooting 56.0% from the field, 33.3% from three-point range and 67.0% from the free throw line. In the SEC, he ranked fourth in points, first in rebounds, third in field goal percentage, fifth in assists, and second in steals.

AWARDS

- McDonald's All-American (2015)