Gabriel will be the third impact receiver added by the Bears once the new league year begins Wednesday, joining former Jaguars wide receiver Allen Robinson and former Philadelphia Eagles tight end Trey Burton.
Gabriel, 27, is known for the speed and big-play ability he displayed in 2016, when he tied Julio Jones for the Falcons' lead with six touchdown receptions. Those scores averaged 42.7 yards as Gabriel typically used his 4.27 speed to break free from defenders.
He caught 33 passes for 378 yards and just one touchdown in 2017 after catching 35 passes for 579 yards with those six scores -- plus a rushing touchdown -- during the Falcons' 2016 Super Bowl run.
Gabriel has averaged more than 16 yards per reception in two of his four NFL seasons.
He entered the league with the Cleveland Browns in 2014 as an undrafted free agent out of Abilene Christian. During his rookie year, he accumulated a career-high 621 receiving yards on a career-best 36 receptions while playing under then-Browns offensive coordinator Kyle Shanahan, now the head coach of the San Francisco 49ers.
Gabriel was released by the Browns before the 2016 season and reunited with Shanahan in Atlanta after the Falcons claimed him on waivers.
ESPN's Vaughn McClure contributed to this report.