Martinez, 52, played 18 seasons for the Mariners from 1987–2004 and holds the franchise records for doubles, RBIs, on-base percentage and total bases.
Johnson spent 2013 as the hitting coach for Seattle's Triple A affiliate and took the same position with parent club in 2014.
The Mariners (31–37) have a team batting average of .233 this season, the worst in the majors. They have the fourth-most strikeouts in the major leagues and their park-adjusted OPS is 10th-worst in the majors.
In recent weeks, Martinez had begun instructing Mariners minor leaguers.
“I had too much time on my hands,” Martinez told The News Tribune of Tacoma, Wash. on June 6. “I always wanted to get back to the game. Right now my family is busy, my wife is working, my kids are all in school and they’re old enough where I can travel more. It’s a good time for me to do it.”
- Dan Gartland