Details of the trade have not been reported. Peters, a two-time Pro Bowler who was named first-team All-Pro in 2016, has compiled an NFL-leading 19 interceptions since being drafted 18th overall three years ago.
The Chiefs are expected to receive draft pick compensation back from the Rams.
He also drew criticism this past year for not standing for the national anthem.
Peters will count $1.74 million toward the salary cap this season, the final year of his rookie deal, and the Rams will have until May 3 to decide whether to pick up his fifth-year option. Peters was dismissed from the Washington Huskies football team in November 2014 for disciplinary issues. While not as proficient at interceptions as Peters, Johnson has picked off 10 passes over the past three years to go along with 41 pass breakups. Simply put, it is a deal that the Rams could reap the benefits from this season and possible further down the line. Peters was suspended one game last season for throwing a penalty flag after a play then left the field without being ejected.
This is the second trade involving a premier player for Kansas City in less than a month.
The new league year doesn't officially kick off until March 14, but already we are seeing some big moves come from the Kansas City Chiefs. They visited with Vontae Davis recently and reportedly had interest in David Amerson before he signed with the Chiefs.
Kansas City does not have a first-round pick in this year's draft. With the added players in the secondary on their way, the Chiefs may have felt they had enough depth to trade Peters.
Schefter later confirmed the news of the trade, which can not be finalized until March 14, the start of the new league year.