He'll be joined by one of the top-rated wide receivers and offensive lineman, forming the foundation for what could be the Rebels' best recruiting class ever. Receiver Laquon Treadwell (Crete, Ill.) and offensive tackle Laremy Tunsil (Lake City, Fla.) also signed with the Rebels on Wednesday.
Nkemdiche, a 6-foot-5, 260-pound defensive end from Loganville, Ga., announced that he will attend Ole Miss during a press conference on ESPNU.
He had been on several programs' wish list for more than a year, but family ties gave Ole Miss the inside track. His brother Denzel Nkemdiche plays for the Rebels and led Mississippi's defense with 82 tackles, including 13 for a loss last season.
Robert Nkemdiche went on an official visit to LSU last week, but when it was all said and done, he signed with the Rebels, donning a red Ole Miss hat after he made the announcement.
"I feel like it's the right place for me," Robert Nkemdiche said during his press conference. "I feel like they can do special things and they're on the rise. I feel like going to play with my brother, we can do something special."
Rivals.com, Scout.com, ESPN, CBS Sports and 247Sports all rated Nkemdiche the top prospect in the country. Treadwell and Tunsil weren't far behind.
Second-year coach Hugh Freeze led Ole Miss to a 7-6 record last season, improving from a 2-10 mark in 2011.
When Nkemdiche, Treadwell and Tunsil announced their decisions, the Ole Miss coaching staff celebrated.
Ole Miss doesn't have the pedigree to usually recruit toe-to-toe with the likes of Alabama, LSU and other Southeastern Conference powerhouse programs. But at least on paper, the Rebels might outshine their SEC opponents when signing day comes to a close on Wednesday.
"I'm so thankful and blessed that these families have chosen to trust in us," Freeze said. "We'll treat these young men as our own."
Wednesday is the first day prep football recruits could officially sign with colleges.
"I feel like he's a good man, he's special," Robert Nkemdiche said of Freeze. "I feel like he's a man of his word. I respect him a lot and I feel like he has good things coming."
He's the first major piece in a class that could be the Rebels' best on paper.
The Rebels are also have a shot at other recruits, including safety Antonio Conner (Batesville, Miss.), defensive end Elijah Daniel (Avon, Ind.) and offensive tackle Austin Golson (Prattville, Ala.).
Denzel Nkemdiche said he and his mother pushed hard for Robert to choose Ole Miss, but ultimately the decision was his. Denzel said his individual success at Ole Miss — along with the big improvement for the program this season — were important factors in Robert's choice.
"The feeling right now is unreal," Denzel Nkemdiche said. "It's real hard to explain. I'm glad it's over. I wanted him to make the right decision that he wanted to make and I wanted him to feel comfortable with the decision he made because he's going to be where he's going to be for the next three years. I'm glad he's going to be there with me. I'll be able to look after him and take some care of him and we'll be able to win the national championship together."