Nielsen previously served in the same position with the Atlanta Falcons in 2023, bringing valuable experience to the Jaguars' coaching staff.

At the Falcons, Nielsen not only served as the defensive coordinator but also excelled as the defensive line coach. During his tenure, the Falcons made significant improvements in their defensive performance. In 2023, the team ranked 18th in points allowed per game, an improvement from the previous year's ranking of 23rd. Similarly, they climbed from 27th in yards allowed to 11th in just one season. The Falcons' ability to register 42 sacks in 2023, compared to 21 in 2022, also showcased Nielsen's coaching expertise.

Prior to his time with the Falcons, Nielsen spent six seasons with the New Orleans Saints from 2017 to 2022. During his tenure, he served as the defensive line coach, contributing to the team's success. Nielsen also took on additional responsibilities, serving as co-defensive coordinator/defensive line coach in 2022 and assistant head coach/defensive line coach in 2021.

Before joining the NFL, Nielsen gained coaching experience at various college teams. He spent four seasons as the defensive line coach at North Carolina State from 2013 to 2016. Additionally, he held coaching positions at Northern Illinois, Tennessee-Martin, Central Connecticut State, Mississippi, and Southern California.

Nielsen's extensive coaching background, coupled with his professional playing experience as a defensive tackle at Southern California from 1997 to 2001, make him a valuable addition to the Jaguars' coaching staff. His expertise and leadership will play a vital role in shaping the team's defense going forward.

The hiring of Nielsen comes after the Jaguars parted ways with previous defensive coordinator Mike Caldwell and made changes to their defensive coaching staff at the conclusion of the 2023 regular season. The Jaguars are hopeful that Nielsen's arrival will bring a new level of success and stability to their defense in the upcoming seasons.