2010-11: Jean-Sebastien Dea played for College Charles-Lemoyne in the Quebec midget AAA league. He scored 26 goals with 29 assists and 28 penalty minutes in 42 regular season games. The Riverains finished fourth in the Reebok Division, and in five playoff games, Dea scored 6 goals with 3 assists and 6 penalty minutes. He was selected by Rouyn-Noranda in the third round (37th overall) of the 2011 QMJHL Entry Draft.
2011-12: Dea skated in 50 regular season games and four playoff contests for Rouyn-Noranda in his first QMJHL season. He scored 17 goals with 15 assists and was -5 with 42 penalty minutes during the regular season. The Huskies finished last in the West Division and were swept by Shawinigan in a first round series. Dea scored 1 goal with 2 assists and was -5 with no penalties against the Cataractes.
2012-13: Dea finished sixth in the QMJHL with 45 goals and was the Huskies' second-leading scorer with 85 points (trailing only Sven Andrighetto (98)) as Rouyn-Noranda finished second in the West Division. Dea was one of two Huskies to skate in all 68 games and was +21 with 59 penalty minutes. Rouyn-Noranda reached the playoff semifinals against Memorial Cup-bound Halifax. Dea led the Huskies with 12 goals and was -2 with 9 assists and 24 penalty minutes in 14 playoff games.
In his second year of draft eligibility, he was ranked 152nd amongst North American skaters in Central Scouting's final rankings but was not selected in the 2013 NHL Draft.
2013-14: Dea was invited to Pittsburgh's training camp as a free agent and was signed to a three-year, entry-level contract with the Penguins in September 2013 before being returned to Rouyn-Noranda for his third season. Dea was tied with Halifax' Nikolaj Ehlers for fourth in the QMJHL with 49 goals. He had 26 assists and was +4 with 53 penalty minutes in 65 games as the Huskies slipped to fifth in the West Division.
Dea will return to the Rouyn-Noranda Huskies for the 2013-14 season.