"What a journey it's been Detroit! Five years of some of the greatest memories of my career," Tulloch wrote.
"Such as life there is constant change. But change that I'm looking forward to. As one chapter closes in my career another one opens up."
The team has yet to make his release official, but it is expected to come next month. He had been the team's starting middle linebacker since coming to Detroit in 2011 after starting his career with the Titans.
Tulloch struggled at points during the 2015 season; in fact, for the first time in his Lions career, he was taken off the field in certain situations. He still led Detroit in tackles with 107 and was a primary player on rushing downs.
He was due $7.3 million in 2016, the final year of his contract. Releasing him should save the Lions about $6 million in cap space.
Tulloch missed the first significant time in his career in 2014 after tearing his ACL while celebrating a sack of Aaron Rodgers in Week 3.
The 31-year-old was selected by the Titans in the fourth round of the 2006 draft out of NC State.
He was among the Detroit players more active in the community, hosting an annual softball tournament and regularly attending community events.