[4][5][6] The youngest of three children, his father, Alex, hailed from the Caribbean island of Guadeloupe and his mother, Nadège, was born in French Guiana in South America.

[6][7] From an early age, Saint-Maximin learnt to speak English, as encouraged by his mother, in order to achieve his dream of playing in the Premier League.

[14] At the age of 16 years, 5 months, and 17 days, he made his club debut on 29 August as a substitute in a Europa League play-off match, coming on for Franck Tabanou before his side suffered a 1–0 loss to Esbjerg fB at Stade Geoffroy-Guichard.

[23] In an interview with France Football he discussed on his departure, stating, "I did everything to impose myself in Sainté with good matches against OM, Bordeaux and Lille.

[32] Following his club bow, Saint-Maximin was benched in the season opener against Darmstadt 98 on 15 August,[33] making his league debut a week later, whilst utilised as an attacking midfielder, in a 1–0 home defeat to Bayer Leverkusen.

[36] In January 2016, during the mid-season break, Saint-Maximin would miss 96's friendly matches in Belek, Turkey, to be with his pregnant wife who was expecting their first child.

[43][44] Saint-Maximin didn't score again until on 10 December, netting a brace in Bastia's 2–0 league victory against Metz, ending their 10 game winless streak.

[48] He played in the final league game for the club on 20 May 2017, after being granted permission from the French Football Federation (FFF) before his call-up to the France U20 squad,[49] in a 1–0 defeat to Marseille at Stade Vélodrome.

However, a stacked attacking depth containing Kylian Mbappé, Rony Lopes and Thomas Lemar, meant he could expect scarce playing time.

"[52] Saint-Maximin made his debut for the club in the 2017 Trophée des Champions against Paris SG, replacing Mbappé in 77th-minute of a 2–1 loss at Ibn Batouta Stadium.

[21] On 7 August 2017, Saint-Maximin completed a move, as a club-record signing, to Côte d'Azur rival Nice for a reported transfer fee of €10 million.

[59] His second goal came two months later in the fourth round of the FA Cup against League One opposition Oxford United, scoring a late winner after a solo run.

[62] On 30 July 2023, Saint-Maximin signed a three-year contract for Saudi Professional League club Al Ahli for a transfer fee reported to be around £23 million.