On July 12, 2018, Oleksiak as a restricted free agent, agreed to a three-year, $6.4 million contract extension with the Penguins.

In the 2018–19 season, on December 19, 2018, Oleksiak fought Washington Capitals forward Tom Wilson in the first period and was briefly knocked unconscious. He left the game and did not return. 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. He was eventually cleared to play on December 29. On January 28, 2019 he was traded back to the Dallas Stars by the Pittsburgh Penguins for the same fourth-round draft pick in 2019 that he was originally traded to Pittsburgh for.

Oleksiak’s first full season in the NHL with Dallas was the 2016–17 season. While waiver eligible, healthy scratches and a hand injury limited Oleksiak to just 41 games. On August 4, 2017, the Stars re-signed Oleksiak to a one-year, $964,688 contract.

In the 2017–18 season, his sixth season within the Stars organization and having been unable to solidify a role on the blueline, Oleksiak appeared in 21 games recording just 3 points before he was traded to the Pittsburgh Penguins in exchange for a conditional fourth-round pick in 2019 NHL Entry Draft on December 19, 2017. Oleksiak immediately established his role with the Penguins and in his 47 regular-season games with the Penguins following the trade, he scored 4 goals, 10 assists for 14 points with increased ice-time. He made his post-season debut with the Penguins, adding 1 goal in 12 games.

Oleksiak’s sister, Penny Oleksiak, is a Canadian competitive swimmer, who won a gold, a silver and two bronze medals in the 2016 Summer Olympics.

On October 28, 2014, Oleksiak scored his first career NHL goal against the St. Louis Blues in a 4–3 loss. He’d finish the season with 8 points in 36 games.

On January 30, 2013, the Dallas Stars called up Oleksiak from the Texas Stars of the American Hockey League. Oleksiak assisted Brenden Morrow for his first NHL point on February 13 vs. Calgary Flames.

Oleksiak attended Northeastern University for one year and had 13 points on 4 goals and 9 assists and team-best +13 plus/minus. After his freshman season with the Northeastern Huskies, Oleksiak decided to return to the Canadian Hockey League for further development, and on July 25, 2011 the Saginaw Spirit announced that they had signed Oleksiak to an Ontario Hockey League contract, and on October 6, 2011, it was announced that Oleksiak had signed a three-year entry level contract with the National Hockey League’s Dallas Stars. With the Spirit out of contention during the 2011–12 season, Oleksiak was traded to the title contending Niagara IceDogs on January 10, 2012.

Oleksiak, who holds dual Canadian/United States citizenship, represented the United States in the 2009 Ivan Hlinka Memorial Tournament which finished in fourth place, but later decided he would represent Canada internationally.

Jamieson Oleksiak (born December 21, 1992) is a Canadian ice hockey defenceman currently playing for the Dallas Stars of the National Hockey League (NHL). Oleksiak was selected 14th overall in the first round of the 2011 NHL Entry Draft by the Stars, the highest draft choice in Northeastern University’s history.