Ramsey started all 14 games for the Florida State Seminoles as a true freshman in 2013. He was the first true freshman to start a game at cornerback for the Seminoles since Deion Sanders in 1985. Ramsey wore the #13 jersey during his freshman year when Florida State won the National Championship over Auburn. He later switched to jersey #8 for his sophomore and junior seasons. Also, Ramsey chose the #17 jersey for kick returns during his junior year, a number that had been retired in honor of former superstar Charlie Ward, who granted Ramsey permission to wear the number. He finished the year with 49 tackles, one interception, and one sack. As a sophomore, Ramsey played 14 games with 80 tackles, two interceptions, 12 passes defended, three forced fumbles, and two sacks. As a junior, he played 13 games with one sack, nine passes defended, and one fumble recovery on 52 tackles. On September 18, against Boston College, he recorded a 36-yard fumble return for a touchdown in the 14–0 victory. He was named as a Consensus All-American for his performance in the 2015 season. After his junior year, he announced his intention to forego his senior season and enter the 2016 NFL Draft.