Simmons, a junior and multiple All-SEC selection, is ranked 16th on ESPN draft expert Todd McShay's Top 32 prospects.
He announced his decision in a letter on the team's website.
In the first-person letter, Simmons seemed to acknowledge the circumstances of his arrival at Mississippi State three seasons ago.
"Not everyone gets a second chance, but I am so grateful I did," Simmons wrote in the first line of the letter.
A top prospect coming out of high school, Simmons was captured on video hitting a woman. He later pleaded no contest to simple assault.
Simmons was allowed to enroll at Mississippi State and was suspended for one game by coach Dan Mullen and athletic director Scott Stricklin, who have both since left for the same positions at Florida.
The 6-foot-4, 300-pound Mississippi native started three games as a freshman that season, becoming an integral part of the defense.
He combined for 26.5 tackles for loss and six sacks the past two seasons.