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 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.