Brennan started at quarterback for LSU in early 2020 but missed most of the past two seasons with injuries.
Brennan had been in a competition with two other people for the starting job.
LSU coach Brian Kelly said that they were grateful for everything that Myles had done for the team. Myles has earned the respect of everyone here through his commitment and love for LSU, and he has made a tremendous impact on this program.
"Myles has always embodied the qualities required to fulfill our mission to graduate champion, and we have full confidence those will help him succeed at every step of his journey as he moves forward."
Brennan was briefly in the transfer portal last winter.
Brennan was persuaded to come back by Kelly after he was hired from Notre Dame.
Daniels entered the portal soon after. "Signing Daniels was one of the more difficult decisions that I made in the off-season," Kelly said in the spring.
Kelly said that it was about competing. The competition on this roster needed to be upgraded.
Daniels threw for over 6,000 yards and 32 touchdown in three seasons as a starter for the Sun Devil.
The quarterbacks threw touchdown passes during LSU's spring game.
Brennan was a fourth-year junior when he got his chance to start in 2020, taking over for Joe Burrow, who had led the team to a national championship the year before.
His season was cut short by a torn muscle.
He broke his arm while fishing.
In December, Max Johnson moved to Texas A&M.
The LSU and Florida State football teams will play in New Orleans.