He is best known as being the son of former New York Jets and Buffalo Bills head coach Rex Ryan.

On January 9, 2017, Ryan was part of the Clemson team that defeated Alabama in the 2017 College Football Playoff National Championship by a score of 35–31.

[6] In 2019 Seth was hired by the Los Angeles Chargers to be a quality control coach[2] as a part of Anthony Lynn's staff.

[5] In 2021 he went with Lynn to the Detroit Lions where he was named the team's assistant wide receivers coach.

In 2022, despite Lynn being fired as offensive coordinator at the end of the 2021 NFL season, Ryan stayed with the Lions and was announced as assistant wide receivers coach.