The value of the one-year deal is $12.476 million, and the sides will work to negotiate a long-term contract once the rules of a new collective bargaining agreement are established.
Because of the NFL's uncertain labor situation, the franchise tag could be dissolved after the current CBA expires at midnight ET Thursday.
Ngata received a non-exclusive tag, meaning he could have negotiated with other teams. But the Ravens held the right to match the offer or receive two first-round draft picks if Ngata signs elsewhere.
The 6-foot-4, 350-pound Ngata was drafted by the Ravens in 2006 with the 12th overall pick. He had 65 tackles and a career-high 5.5 sacks this past season and made the Pro Bowl for a second consecutive year.
Ngata has missed just two games in his five seasons with the Ravens.
The previous two players to be franchised by the Ravens, linebacker Terrell Suggs and cornerback Chris McAlister, received long-term contracts from the team. Ravens coach John Harbaugh said after the season-ending playoff to the Pittsburgh Steelers that keeping Ngata was "priority No. 1," and general manager Ozzie Newsome later reiterated that point.
The Associated Press contributed to this report.