Sissons joined the Kelowna Rockets for the 2010–11 season, his rookie season. During the season, he recorded a hat-trick on February 16, 2011, to help the Rockets jump into first place in the WHL BC division. The goals, which were his 12th, 13th, and 14th of the season, also helped the Rockets improve to 32–23–0–1 in the season. In March, Sissons missed three games for the Rockets while recovering from a leg injury. At the conclusion of the season, Sissons won the Rockets' Rookie of the Year Award and Plus/Minus Award. He was also invited to participate in the NHL Research, Development and Orientation Camp. In his first year of NHL draft eligibility, Sissons finished his second season in the WHL with 26 goals, including a team-leading 13 power play, through 58 games as the Rockets finished in sixth place in the Western Conference. He was named captain of Team Orr for the CHL/NHL Top Prospects Game after tallying 25 goals and 36 points through 48 games. Leading up to the 2012 NHL Entry Draft, Sissons was ranked 14th amongst all North American skaters by the NHL Central Scouting Bureau. He was eventually drafted 50th overall by the Nashville Predators and signed a three-year entry-level contract with the team. Sissons was returned to the Rockets for the 2012–13 season, where he scored 28 goals and 39 assists through 61 games. During the season, he was invited to participate in Team Canada's national junior team training camp but had to pull out after suffering a left arm injury. Despite this, he was named the Rockets MVP and top defensive forward for the season. Professional After attending the Predators' 2013 training camp, Sissons was re-assigned to their American Hockey League (AHL) affiliate, the Milwaukee Admirals, for the 2013–14 season. While centering the Admirals first line, he tallied his first professional point, an assist, in his debut game. Prior to turning 20, Sissons had recorded four goals and two assists in his first eight games to be tied for second in scoring across the team. His maturity earned him praise from Admirals coach Dean Evason, who said: "It's as if he's been a 10-year pro in how he goes about his business, how he prepares for games, and how he is with his teammates off the ice." As the season continued, Sissons continued to produce and recorded a five-game point streak from November