To make room on the 25-man roster, outfielder Carlos Peguero was optioned to Triple-A Tacoma.
Saunders has been on the disabled list since April 11 with a sprained right shoulder after crashing into the right-field wall at Safeco. In nine games this year, he's hit .286 with one home run and five RBIs.
Saunders' return is critical for a Mariners team that also has center fielder Franklin Gutierrez on the 15-day disabled list with a right hamstring strain.
In three rehab appearances with Tacoma over the weekend, Saunders went 2-for-11 (.182) with two runs, one double, one triple and two RBIs.
Saunders said he was able to cut loose with his shoulder and passed all the necessary tests to ensure he was ready.
"You get out there and your competitive nature takes over," he said. "You're not so tense. I learned in '08 [when coming back from shoulder surgery] that the last 5-10 percent is mental and just trusting that you're healthy and ready to do it. Once I was at the plate, I took hard swings and it felt good to let it go."
Saunders said he would play the same aggressive way he did before slamming into the wall tracking down a Jose Altuve line drive.
"There's no point in playing scared," he said. "I'm out there to play hard and that's the way I've always played. That was one of the tests, to make sure I felt like myself."
Peguero played in two games with the Mariners, batting .333 (2-for-6) with a home run and a stolen base.
Greg Johns is a reporter for MLB.com. Follow him on Twitter @GregJohnsMLB as well as his Mariners Musings blog. This story was not subject to the approval of Major League Baseball or its clubs.