2010-11: Jacob Sweeney skated for the midget AA Cyclones in Quebec City. He was selected by Victoriaville in the first round (15th overall) in the 2011 QMJHL Entry Draft.
2011-12: Sweeney appeared in nine QMJHL games — spending most of the season playing in the Quebec midget AAA league with the Seminaire St-Francois Blizzard. He was -3 in three games with the Victoriaville Tigres before being one of the players sent to Moncton in exchange for 19-year-old defenseman Dan Milan (TB) in a January trade. Sweeney had 1 assist and was -2 in six games with the Wildcats. In 34 regular season games for Seminaire St-Fracois he scored 2 goals with 7 assists and had 24 penalty minutes. Sweeney scored 1 goal with 5 assists and had 4 penalty minutes in 20 playoff games as the Blizzard reached the Quebec finals against College Esther-Blondin.
2012-13: Sweeney played in 63 of 68 games for Moncton in his first full QMJHL season. He scored 2 goals with 5 assists and was +14 with 14 penalty minutes. The Wildcats finished second in the Maritimes Division before falling to Victoriaville in a first-round playoff series. Sweeney was -1 with no points and 2 penalty minutes in five playoff games. He was ranked 189th amongst North American skaters in Central Scouting's final rankings prior to the 2013 NHL Draft and was not selected.
2013-14: Sweeney returned to Moncton for his second season and was the Wildcats' leading scorer amongst defensemen. In 68 games he scored 3 goals with 25 assists and was -15 with 57 penalty minutes. The Wildcats finished third in the QMJHL's Maritimes Division.
In his second year of eligibility, Sweeney's stay-at-home play has been boosted by the addition of some offensive flavour to his toolbox. In his own end, he uses his long reach and physical tools to shut down the opposition. Meanwhile, his work in the offensive end is developing, showing some good puck-moving ability and a willingness to join the rush. Passed over in his draft year, Sweeney's overall game is raw and aspects of it, like his mobility, still need further refinement. But his natural tools, like his size and his focus on improvement, cannot be ignored.