Baltimore dealt its 2010 third- and fourth-round draft picks to the Cardinals in exchange for Boldin and a 2010 fifth-round draft pick, the Ravens said in a release Friday.
Boldin had 84 catches for 1,024 yards and four touchdowns last season while helping the Cards win the NFC West with a 10-6 record.
Over his seven-year NFL career, spent entirely with the Cardinals, the 6-foot-1, 217-pound Boldin has 586 receptions for 7,520 yards and 44 touchdowns.
"I really look at this as a great opportunity for me," said Boldin. "They love football in Baltimore. I know that from when the Cardinals played there a few years ago.
"That place was loud, very impressive by the fans. The Ravens play a certain way. They play as hard and as physical as any team in the league, and I want to add to that.
"I think I play the way they play."
Boldin is the Cardinals' all-time leader in receptions.
(Writing by Steve Ginsburg)