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.
Ihedigbo, a six-year veteran out of UMass, was vying for a backup job behind starters Patrick Chung and Steve Gregory this year, but the emergence of rookies Tavon Wilson (second round) and Nate Ebner (sixth round) made him expendable.
Ihedigbo, who joined the Patriots in August 2011, was a surprise contributor on defense last season. Initially thought to be more of a special teams presence, he ended up playing 67 percent of the defensive snaps last season, in part because of injuries to others and the release of veterans James Sanders and Brandon Meriweather at the end of the preseason.
After going undrafted 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.