Neither team revealed the terms of the deal, but the Detrot Free Press said the Lions gave up draft picks in the fourth and fifth rounds.
Ngata, 31, among the NFL’s premier defensive linemen, played nine seasons with Baltimore, collecting 528 tackles, 25 1/2 sacks, and five interceptions.
“Haloti has been an outstanding player for us for many years,” Ravens General Manager Ozzie Newsome said. “He consistently showed tremendous leadership in our locker room and on the field. At times, he was one of the NFL’s most dominant players.”
Ravens Coach John Harbaugh called Ngata the “anchor of our success for many years.”
Baltimore reportedly was considering releasing Ngata because of the $16 million he counts against the team’s salary cap, but instead found a trade partner in Detroit.
Follow Sam Farmer on Twitter @LATimesFarmer