Internationally Roussel has represented the French national team both at the junior and senior level, including multiple World Championships.

He first played rugby as a child, but was released from his team after repeatedly running off the field during the heated summer practices.

[5] Undrafted in the NHL Entry Draft, Roussel signed an AHL contract on 9 August 2010 with the Providence Bruins, where he played the 2010–11 season.

[7] His performance there led to him signing a contract with the Chicago Wolves, which at the time were the Canucks' minor league affiliate in the AHL.

[11] After six seasons with the Stars, Roussel left as a free agent and on 1 July 2018, he signed a four-year, $12 million contract with the Vancouver Canucks.

[12] Roussel set a career-high in points in 2018–19 with the Canucks, with 31, before suffering a season-ending knee injury on 13 March 2019, during a game against the New York Rangers.

Expected to miss the first two months of the season,[14] Roussel made his return to the lineup on 3 December in a 5–2 win over the Ottawa Senators, scoring two goals, including one on his first shift since the injury.