The 2021 Marshall Thundering Herd football team represented Marshall University during the 2021 NCAA Division I FBS football season. The Thundering Herd played their home games at the Joan C. Edwards Stadium in Huntington, West Virginia, and competed in the East Division of Conference USA (CUSA). The team was coached by first-year head coach Charles Huff.
On October 30, 2021, Marshall announced they would become a member of the Sun Belt Conference. On March 29, it was announced they would officially join on July 1, 2022, making this the final season competing in C-USA.
Marshall announced its 2021 football schedule on January 27, 2021. The 2021 schedule consists of 6 home and 6 away games in the regular season.