He played college football for the Florida State Seminoles and was selected by the Jacksonville Jaguars fifth overall in the 2016 NFL draft.

With the Jaguars, Ramsey quickly became one of the top cornerbacks in the NFL, making the Pro Bowl and being named an All-Pro in 2017, in addition to helping Jacksonville snap a 10-year playoff drought.

However, following a fallout and standoff with the Jaguars' front office, he was traded to the Los Angeles Rams midway through the 2019 season.

In 2020, he agreed to an extension with the Rams that made him the highest-paid defensive back in league history at the time.

[14][15] Ramsey wore jersey #13 during his freshman year when Florida State won the National Championship over Auburn.

[17] As a sophomore, Ramsey played 14 games with 80 tackles, two interceptions, 12 passes defended, three forced fumbles, and two sacks.

[22] After his junior year, he announced his intention to forgo his senior season and enter the 2016 NFL draft.

He was a three-time All-Atlantic Coast Conference (ACC) honoree as a member of the Florida State Indoor and Outdoor championship track and field team in 2013.

He was considered to be a top ten pick by NFL media analysts Daniel Jeremiah, Charles Davis, and Mike Mayock.

[29] On March 29, 2016, he chose to participate at Florida State's pro day, along with Roberto Aguayo, Lamarcus Brutus, Terrance Smith, and 20 other prospects.

Team representatives and scouts from 31 NFL teams attended, with the Cincinnati Bengals opting not to, and among them included general managers Doug Whaley (Bills), Kevin Colbert (Steelers), Jason Licht (Buccaneers), Jon Robinson (Titans), and Steelers' head coach Mike Tomlin.

[42] Ramsey made his NFL debut and first start in the season-opener against the Green Bay Packers and recorded three solo tackles in the 27–23 loss.

[43] During a Week 8 against the Tennessee Titans, he made a season-high eight combined tackles as the Jaguars lost on the road by a score of 36–22.

[44] On December 18, 2016, Ramsey collected four solo tackles, a season-high five pass deflections, a forced fumble, and recorded his first NFL interception by picking off Brock Osweiler in a 21–20 road loss to the Houston Texans.

[46] The next week, under interim head coach Doug Marrone, Ramsey made four solo tackles, defended four passes, and intercepted Matt Cassel and returned it for a touchdown, helping the Jaguars defeat the Titans by a score of 38–17.

[47] Ramsey was named American Football Conference (AFC) Defensive Player of the Week for his performance against the Titans.

[48] Ramsey finished his rookie season with 65 combined tackles (55 solo), 14 pass deflections, two interceptions, and a touchdown in 16 games and 16 starts.

[49] Pro Football Focus (PFF) gave Ramsey an overall grade of 82.3, which ranked 21st among all qualifying cornerbacks in 2016.

[51] Ramsey returned as the Jaguars' de facto starting cornerback and joined a revamped secondary that included A. J. Bouye, Aaron Colvin, Barry Church, and Tashaun Gipson.

[58] Ramsey started all 16 games in 2017 and made 63 combined tackles (52 solo), 17 pass deflections, and four interceptions.

His interception came late in the fourth quarter when he picked off Bills' quarterback Nathan Peterman, who had just entered the game for the injured Tyrod Taylor, and sealed the win for the Jaguars.

[65][66] In the Divisional Round against the Steelers, he finished with four total tackles in the 45–42 road victory at Heinz Field.

He was named to his second Pro Bowl, where he switched positions and caught a receiving touchdown from Houston Texans quarterback Deshaun Watson in the fourth quarter.

[75] Ramsey started the Jaguars' first three games, totaling 13 solo tackles with a pass deflection and a forced fumble.

[79][80] During Week 16 against the San Francisco 49ers on Saturday Night Football, Ramsey recorded his first interception of the season off a pass thrown by Jimmy Garoppolo in the first quarter during the 34–31 road loss.

In the final minute on third and 16, he and safety Taylor Rapp made an error in coverage which resulted in a 46-yard completion to wide receiver Emmanuel Sanders, eventually leading to the game-winning field goal which knocked the Rams out of playoff contention.

[114] On September 6, 2024, Ramsey agreed to a three-year, $72.3 million extension with the Dolphins, making him the highest-paid cornerback in the NFL.

[120] In an August 2018 interview with GQ, Ramsey also offered his unfiltered opinions of several NFL quarterbacks, criticizing Joe Flacco, Josh Allen, Andrew Luck, Eli Manning, Ben Roethlisberger, Matt Ryan, Jared Goff, among others.