He becomes the eighth member of the Mariners HOF, joining Jay Buhner, Alvin Davis, Ken Griffey Jr., Randy Johnson, Edgar Martinez, Dave Niehaus and Dan Wilson - some of whom will be present at the 5:30 p.m. pregame ceremony.
Piniella, 70, is the winningest manager in Mariners history - and, in fact, is the only skipper to have an overall winning record at 840-711. He managed Seattle from 1993 through 2002, leading the M's to their first-ever postseason appearance in 1995 and additional trips to the playoffs in 1997, 2000 and 2001.
The M's haven't been back to the postseason since, but are in the hunt this season after nearly a decade of mediocre baseball.
On Saturday, the first 20,000 fans to Safeco Field will receive a Piniella bobblehead. First pitch is scheduled for 6:10 p.m.