Christensen played four seasons with Everett of the Western Hockey League and began his professional career in 2019-20 playing on a professional tryout with Stockton (Calgary Flames).
After nine AHL games he was returned to Everett and scored 50 points (22 goals, 28 assists) in 38 games. His average of 1.32 points per game led WHL defensemen and he signed a three-year, entry-level contract with the Blue Jackets on March 4, 2020.
Christiansen (6-0, 186) scored 15 points (three goals, 12 assists) in 28 games with Cleveland last season. This season, the 22-year-old is second among AHL defensemen with 17 points (five goals, 12 assists) in 17 games.