Jackson, 30, had received nothing but praise from the Browns' new leadership, but apparently that was not enough to overcome $4.1 million in bonuses due Jackson on March 15.
The team put out a release describing the decision as mutual, but late last season Jackson said the thought of leaving had not entered his mind and he expected to be back. Jackson, however, became one of the most vocal critics of the decision to fire Rob Chudzinski as coach after only one season.
The Browns' statement said the team and Jackson's agent, Brian Mackler, had "positive discussions" the past few days but came to a mutual decision to part ways.
"D'Qwell is the epitome of class, leadership and professionalism," general manager Ray Farmer said in a statement released by the team. "Every day of his NFL career, D'Qwell has been a solid representative of the Browns and the city of Cleveland, both between the lines on Sundays and off the field in our area community."
Jackson released a statement thanking fans for their support.
"It's been an honor playing in front of you," he wrote.
Tributes from teammates also poured into Twitter.
"DQ is a leader of men," tight end Jordan Cameron posted. "Gave me confidence when I had none and listened when I needed someone. Most underrated player in the NFL."
Jackson was a second-round choice of the Browns in 2006. He led the team with 139 tackles in 2013.
His salary cap cost had been slated to be $8.1 million, with the linebackers in total accounting for $24 million of the salary cap. The timing of the moves means Jackson can find a new home before free agency starts March 11.