An NFL source told ESPN NFL Insider Adam Schefter that the contract is worth $132 million and includes $60 million guaranteed. Johnson's contract is the richest deal ever for an NFL wide receiver, exceeding the $120 million deal Larry Fitzgerald signed with the Arizona Cardinals last year.
The extension puts Johnson under contract with the Lions through the 2019 season. The team is holding a news conference at 1 p.m. ET.
He was set to enter the final season of the deal he signed as the No. 2 pick overall in the 2007 draft.
Johnson earned All-Pro honors for the first time last season with a league-best 1,681 yards receiving. He followed up with 211 yards receiving against New Orleans in the playoffs, setting a league record for a player in his postseason debut.