Oleksiak played a total of 16 games for the Dallas Stars during the 2012–13 season, accumulating two assists, 14 penalty minutes and 11 shots.[23] In the final year of his entry-level contract, Oleksiak dipped in production at the AHL level but tallied eight points through 36 games with the Dallas Stars in the NHL.[25] Oleksiak scored his first career NHL goal on October 28, in the first period of an eventual 4–3 overtime loss to the St. Louis Blues.[35] Due to injuries to three of the Stars' top six defensemen, head coach Lindy Ruff opted to give Oleksiak, Kris Russell, Alex Goligoski, Johnny Oduya, and Patrik Nemeth longer minutes during games throughout March.During the offseason, the Stars parted ways with veteran defencemen Alex Goligoski, Jason Demers, and Kris Russell, leaving an opening for Oleksiak to earn more playing time.[39] He quickly made use of this opportunity and impressed head coach Lindy Ruff while paired with Esa Lindell in mid-October.[40] However, he became a healthy scratch once again and missed nine games since October 20 before rejoining the lineup on November 10 as the Stars experienced a three-game losing streak.[42] He subsequently missed 13 games before returning on February 11 to play alongside Stephen Johns in a 5–2 win against the Carolina Hurricanes.[47] As the season continued, he was used largely on the team's bottom defensive pairing alongside Ian Cole, Matt Hunwick, or Chad Ruhwedel.[52] After evaluation, the team announced that Oleksiak had suffered a concussion as a result of the fight and would be sidelined from game action indefinitely.[56] As the Stars clinched a playoff berth, Oleksiak returned to the lineup while key players sat out of back-to-back games in order to rest.[57] While playing as a third-pairing defenseman along with Taylor Fedun, Oleksiak tallied an assist on Tyler Seguin's goal to help the Stars clinch the top wildcard spot in the 2019 Stanley Cup playoffs.[60] While playing alongside Ben Lovejoy,[61] Oleksiak and the Stars eliminated the Predators in six games to advance to Round 2 of the Stanley Cup Playoffs.[65] Oleksiak quickly became one of the most active Stars player in the offensive zone as he helped dominate scoring chances with Miro Heiskanen in a top four role.Despite missing four games due to a lower-body injury, Oleksiak led all Seattle defensemen in goal scoring by late November.[78] Twelve years later, Oleksiak accepted an invitation to make his senior national team debut at the 2024 IIHF World Championship.[80][81] He attended school with both Dougie and Freddie Hamilton at Crestwood Preparatory College in Toronto, Ontario, before moving to the United States to pursue his career in hockey.