Watkins, 27, could help the Ravens improve their league-worst passing game. He has 321 receptions for 4,664 yards and 33 touchdowns in his career.
He picked the Ravens for a chance to play with another former NFL MVP and a chance to win a Super Bowl.
“Honestly, (Baltimore) feels like Kansas City to me; feels like a team that’s ready to win the Super Bowl,” Watkins said, via John Eisenberg of the team website. “A team that’s ready to win and go out there and have fun and put up points. Good defense, good special teams. I’m just happy to be here and be involved with a good organization.”