Conley, 26, started 34 games in his four seasons with the Kansas City Chiefs since he arrived as a third-round pick (76th overall) from Georgia in 2015. Thirteen of those starts came in 2018, when Conley caught 32 passes for 334 yards and five touchdowns.
He set career highs in 2016, when he caught 44 passes for 530 yards. In his four seasons, Conley has caught 104 passes for 1,238 yards and six touchdowns.
Conley was limited to five games in 2017, when his season ended prematurely because of a ruptured Achilles tendon.
In addition to Conley, the Jags also announced that they have signed former Cincinnati Bengals offensive lineman Cedric Ogbuehi. A former first-round pick of the Bengals, the 26-year-old Ogbuehi spent most of last season as a healthy scratch for a Cincinnati team that finished the season 6-10.
The Jags did not reveal contract terms for Ogbuehi or Conley.
Jacksonville also has agreed to terms with linebacker Jake Ryan, sources told ESPN's Rob Demovsky, confirming multiple reports.
Ryan, a fourth-round pick in 2015, tore his ACL in training camp last summer with the Green Bay Packers and missed the entire season, but should be ready for the start of the 2019 season.
He had been penciled in to start at inside linebacker alongside Blake Martinez, and the Packers never found a permanent replacement for him last season.
ESPN's Adam Teicher and Rob Demovsky contributed to this report.