Ihedigbo started 12 games last year for the Patriots in 2011. He had 69 tackles and one pass deflection.
The 28-year-old made the announcement Sunday on his personal Twitter page.
"Fresh start...God is good...honored to be a Baltimore Raven!!!! #blackandpurple," he tweeted.
After going undrafted out of the University of Massachusetts in 2007, Ihedigbo signed with the New York Jets and spent his first four NFL seasons there. After playing with New England in 2011, he was re-signed this past June before being released this past Friday.