Johnson, 27, will earn nearly $17 million this season and then will become an unrestricted free agent.
Johnson was one of three NFL players with the franchise tag who did not come to terms with their teams. Washington quarterback Kirk Cousins and Pittsburgh running back Le’Veon Bell also will play under the franchise tag, Cousins for the second time.
Cousins will earn nearly $24 million this season, Bell about $12 million.
Chargers linebacker Melvin Ingram, Arizona Cardinals linebacker Chandler Jones, New York Giants defensive lineman Jason Pierre-Paul and Carolina Panthers defensive lineman Kawann Short were franchise-tagged players who signed new contracts in March, April and June.
Johnson, a third-round draft pick in 2012, has intercepted 16 passes in five seasons with the Rams, including a career best seven in 2015.
After that season, the Rams opted to put the franchise tag on Johnson — at a cost of nearly $14 million — and let cornerback Janoris Jenkins become a free agent. Jenkins signed a five-year, $62.5-million deal with the New York Giants. He intercepted three passes last season and was selected to the Pro Bowl.
Johnson, slowed by an ankle injury that sidelined him for two-plus games, intercepted only one pass last season. He leads a Rams secondary that also includes cornerbacks Kayvon Webster, E.J. Gaines, Nickell Robey-Coleman, Troy Hill and Mike Jordan among others.
The Rams open training camp on July 29 at UC Irvine.
Johnson’s contract situation for this season has been finalized, but Rams salary-related drama is expected to continue.
Three-time Pro Bowl defensive tackle Aaron Donald wants a new contract that would make him one of the highest-paid defensive players in the NFL.
Donald is scheduled to earn $3.2 million in salary and bonuses this season and about $6.9 million in 2018.
Follow Gary Klein on Twitter @latimesklein