He has previously played for the Columbus Blue Jackets, Tampa Bay Lightning, Florida Panthers, and the Vegas Golden Knights.

[11][17][18][19] Not having been selected in any NHL Entry Draft, on June 23, 2011, Marchessault signed his first professional contract with the New York Rangers' American Hockey League (AHL) affiliate, the Connecticut Whale, on a recommendation by Dean Stork, coach of the ECHL's Greenville Road Warriors.

[27] After the 2011–12 season, Marchessault did not re-sign with the Whale, instead signing a three-year, entry-level contract as a free agent with the Columbus Blue Jackets.

[32] On April 11, 2015, the Lightning called Marchessault up from the AHL's Syracuse Crunch to replace an ill Jonathan Drouin in the final game of the regular season.

[33] On April 11, he scored his first career NHL goal and point in a Tampa Bay's 3–2 shootout victory over the visiting Boston Bruins; he was also named the game's first star by the attending media.

[35] After the Crunch were eliminated from the AHL playoffs, Marchessault was recalled to practice with the team as one of the "Black Aces," an extra player to fill in for possible injuries on the roster.

[37] After three seasons within the Lightning organization, Marchessault left as a free agent and signed a two-year, one-way contract with the Florida Panthers on July 1, 2016.

[41] He scored 25 goals to go with 34 assists during the 2018–19 NHL season, as the Golden Knights once again battled the San Jose Sharks in the 2019 Stanley Cup playoffs.

Afterwards, he was very outspoken about the major penalty call in the third period to teammate Cody Eakin, who cross-checked Sharks forward Joe Pavelski who fell to the ice awkwardly and subsequently began bleeding from his head.

[44] The 2021–22 season proved a disappointment for the Golden Knights, plagued by injuries to key players, ultimately missing the playoffs for the first time in franchise history.

In a Conference Final rematch against the Dallas Stars, Marchessault managed a late tying goal in Game 2, sending it to overtime where the Golden Knights emerged victorious.

[49] Continuing to score prolifically, many in the media began to suggest that Marchessault would be the favorite for the Conn Smythe Trophy as the most valuable player of the postseason were the Golden Knights to win.

Marchessault tied the Oilers' Leon Draisaitl for first place in goal-scoring in the playoffs (13) and was second in points (25), one behind teammate Jack Eichel, earning as a result the Conn Smythe Trophy.

[53] Following a 2023–24 season that saw him record a career-high 42 goals, Marchessault left the Golden Knights as a free agent and signed a five-year, $27.5 million contract with the Nashville Predators on July 1, 2024.

[54] On April 29, 2019, Marchessault was selected to his maiden international tournament after he was named to the Team Canada roster for the 2019 IIHF World Championship, held in Slovakia.