Christiansen grew up on a horse farm in Suffolk, Virginia, and attended Nansemond-Suffolk Academy, where he played football and lacrosse.

[5] Christiansen signed with the Los Angeles Chargers as an undrafted free agent on April 25, 2020, after receiving a waiver that allowed him to serve in the reserves and delay his active duty commitment until after his playing career is over.

[7] He was waived by the Chargers during final roster cuts on September 5, 2020, but was signed to the team's practice squad the next day.

[13] On August 31, 2021, Christiansen was waived by the Chargers and re-signed to the practice squad the next day.

[17] On September 1, 2022, Christiansen was signed to the Kansas City Chiefs practice squad.

[24] The Chiefs withdrew Christiansen's exclusive rights tender on May 4, 2024 making a free agent.