He took the Rock-A-Chaws to state title game appearances in 2014 and 2015, both losses to Noxubee County, where he faced future Tennessee Titans defensive end Jeffery Simmons.

[8] In 2019, Brennan played in 10 games and completed 24 of 40 passes for 353 yards with a touchdown, as the Tigers won the national championship.

Opposing MSU quarterback K. J. Costello threw for 623 yards, setting a new SEC single-game passing record.

[13] Following a season-ending injury suffered by Brennan during preseason training camp, Max Johnson was named LSU's starting quarterback.

[15] After opting to remain at LSU, Coach Brian Kelly announced on August 15, 2022, that Brennan has chosen to end his football career.