[2] Fournier was born on 29 October 1992, in Saint-Maurice, a small suburb outside of Paris, to a French father and a mother of Algerian descent.

[11] On 26 June 2014, Fournier was traded, along with the draft rights to Devyn Marble, to the Orlando Magic in exchange for Arron Afflalo.

[16] In 2015–16, Fournier had a career year in which he averaged personal highs in scoring (15.4 ppg), rebounding (2.8 rpg), assists (2.7 apg), steals (1.2 spg) and minutes (32.5 mpg).

[24] On 25 March 2021, Fournier was traded to the Boston Celtics in exchange for Jeff Teague and two future second round draft picks.

[25][26] Fournier had played and started in 26 games and was averaging 19.7 points, 2.9 rebounds, 3.7 assists and 1.0 steals, while shooting 38.8 percent from three-point range with the Magic for the season.

[33][34] On 20 October, Fournier made his Knicks debut, tying a career-high 32 points in a 138–134 double overtime win over his former team, the Boston Celtics.

[35] On 6 January 2022, Fournier surpassed that career-high, scoring 41 points behind ten three-pointers, along with eight rebounds, in a 108–105 victory over the Celtics.

[37] On 8 February 2024, Fournier, Ryan Arcidiacono, Malachi Flynn, Quentin Grimes and two second-round picks were traded to the Detroit Pistons in exchange for Bojan Bogdanović and Alec Burks.