"We have worked diligently to develop and retain talent over the years, and these contracts keep two of our best players with us for the foreseeable future," coach Marvin Lewis said in a statement.
The Bengals made extensions for their top two defensive players a priority. Dunlap didn't participate in some offseason team activities, forcing the issue before the sides got immersed in extension talks.
The Bengals cleared some salary cap room for the deals when they released receiver Brandon LaFell and safety George Iloka during training camp, opening spots for younger and less-expensive players.
Atkins, 30, made his sixth Pro Bowl and led the Bengals with nine sacks last season, the most by an NFL interior lineman. He has 61 sacks in his eight seasons, the most by a Bengals interior lineman.
Dunlap, 29, finished third on the club with 7½ sacks last season. His best year was 2015, when he had 13½ sacks, second-most in club history. His totals have slipped each of the past two seasons. He's also adept and blocking passes at the line, knocking down a team-leading 15 in 2016.