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.
Upon signing, Marchessault joined former Rempart teammates Ryan Bourque and Kelsey Tessier within the Rangers organization.
Marchessault began his professional career in 2011–12 with the Whale.

On October 9, 2011, in his second professional game, Marchessault scored the game-winning shootout goal against the Wilkes-Barre/Scranton Penguins.
He scored his first professional non-shootout goal on October 22, 2011, in a game against the Springfield Falcons.
In his first professional season, Marchessault tied for the Whale team lead with 64 points, leading the team with 40 assists and adding 24 goals.
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. Upon signing, Marchessault joined former Rempart teammates Ryan Bourque and Kelsey Tessier within the Rangers organization. Marchessault began his professional career in 2011–12 with the Whale.
On October 9, 2011, in his second professional game, Marchessault scored the game-winning shootout goal against the Wilkes-Barre/Scranton Penguins. He scored his first professional non-shootout goal on October 22, 2011, in a game against the Springfield Falcons. In his first professional season, Marchessault tied for the Whale team lead with 64 points, leading the team with 40 assists and adding 24 goals.
Jonathan Marchessault