Mounié is a Montpellier HSC youth academy graduate. He made his first team debut on 28 October 2014 in a 2014–15 Coupe de la Ligue round of 32 home match against AC Ajaccio, replacing Jean Deza after 86 minutes; Montpellier lost the match 1–0.
On 11 March 2017, Mounié scored for the fifth consecutive Ligue 1 match by opening the scoring in the 12th minute in the 3-2 home Ligue 1 loss to Nantes; it was his 13th Ligue 1 goal of the season.
On 31 August 2015, Mounié was loaned to Nîmes Olympique for the rest of the 2015–16 season. He was the club's top scorer for the 2015–16 season, with 11 goals in 33 competitive matches, all of them scored during the 2015–16 Ligue 2 campaign.
On 5 July 2017, Mounié joined newly-promoted Premier League club Huddersfield Town on a four-year deal for a club record fee of €13 million (£11.5 million) plus add-ons. The £11.5 million transfer fee surpassed the previous record £8 million (initial fee) that Huddersfield Town spent in buying Aaron Mooy from Manchester City on 30 June 2017.
|Nîmes (loan)||2015–16||Ligue 2||32||11||1||0||0||0||—||33||11|
|Huddersfield Town||2017–18||Premier League||4||2||0||0||0||0||—||4||2|
|1.||23 March 2016||Juba Stadium, Juba, South Sudan||South Sudan||2–0||2–1||2017 Africa Cup of Nations qualification|