Robey, a three-year starter for the Trojans, said he made his decision a few days ago and informed Coach Lane Kiffin.
“He respected my decision,” Robey said. “It’s a business decision, like any other important decision I’ve made my whole life.
“It’s the best thing for my family and for me.”
Robey is the second USC player with eligibility remaining to declare for the draft. Receiver Robert Woods announced immediately after the Trojans’ Sun Bowl loss to Georgia Tech that he was turning pro.
The 5-foot-8, 165-pound Robey said he had submitted paperwork to the NFL and that he had been invited to participate in the NFL Scouting Combine.
Robey, who came to USC from Frostproof, Fla., said last month that an evaluation from the NFL did not project him being selected in the first three rounds.
But Robey said he was not deterred from pursuing his dream of playing in the NFL.
“This is an opportunity,” he said. “Nothing is guaranteed to anybody. They can make a lot of predictions, but nothing is guaranteed.”
Robey had 52 tackles and intercepted one pass this season as teams threw away from his side. He intercepted seven passes in three seasons.
Robey thanked USC and Trojans fans for their support during his career. He said Kiffin was supportive of his decision.
“He took it very professionally,” Robey said. “He didn’t say, ‘Don’t go.’
“He wished me the best of luck and thanked me for coming to USC.”