Jansen was born on May 23, 1997, in Cleveland, Ohio. Born in Cleveland, Ohio, Jansen grew up in North Vancouver and has competed internationally for Canada. Following his time with the Vancouver Giants U18 program, Jansen was drafted second overall in the 2012 WHL Bantam Draft by the Prince George Cougars. He went on to play four seasons with Prince George and was an assistant captain for three of those years. In 2015, the Winnipeg Jets drafted Jansen in the second round, 47th overall. He made his NHL debut on December 21st, 2019, tallying an assist in a win over the Minnesota Wild. As of the 2020-21 season, Jansen has played 55 NHL games.