"Brendon was the first player we signed when we arrived in 2008, and he went to the Pro Bowl again that season," Harbaugh said in the team's statement. "We considered him one of the foundations of our team, and he gave me sound counsel as one of our team leaders.
"He was a tremendous contributor to our success, both on [special] teams and for our defense over the last five seasons, including our Super Bowl [victory] two months ago. And, he was a pleasure to have on our team. We'll stay in contact, I hope, but I'll miss our regular conversations."
A 10-year veteran, the 36-year-old Ayanbadejo played primarily on special teams for the Ravens.
He had a career-high 30 tackles from scrimmage last season for the Super Bowl champions. He also had a sack and 14 stops on special teams.
Ayanbadejo made the Pro Bowl in his first season with the Ravens after also making it twice while with the Chicago Bears.
"I would like to thank the city of Baltimore and the Ravens organization for an amazing ride. We will forever be united as champions!" Ayanbadejo wrote Wednesday on Twitter.
In addition to the football field, Ayanbadejo has made headlines off it. He has been a highly visible defender of gay rights and same-sex marriage.
The Baltimore Sun reported that Ayanbadejo's release puts the Ravens approximately $6 million under the salary cap. According to the newspaper, he was scheduled to make $940,000 in base salary in 2013 as part of a three-year, $3.22 million contract he signed last year.
General manager Ozzie Newsome hinted that Ayanbadejo could be re-signed at a later date.
"As a team, we place a high value on special teams, and Brendon was one of our top performers in that area for the last five seasons," Newsome said in the statement. "He was one of the best special teamers in the league, but he was also a valued member of our defense, especially in our sub packages. He became a leader for us, and the door may not be closed to bring him back to help us again."
Information from The Associated Press was used in this report.