Pistons general manager Troy Weaver and Gross completed negotiations on the deal at summer league in Las Vegas, sources said. This is the Pistons' first rookie extension since owner Tom Gores purchased the franchise in 2011 -- and the first for the organization since Jason Maxiell in 2008.
Stewart, 22, has emerged as an integral part of the Pistons' rebuild. Stewart averaged 11.3 points and 8.1 rebounds, starting 47 of 50 games before suffering a season-ending left shoulder injury in early March. Stewart had a career-high 13 double-doubles last season, according to ESPN Stats & Information research.
The Pistons did re-sign center Andre Drummond on a five-year, $127 million deal in 2016, but that was as a restricted free agent, not a rookie extension.
Stewart is the first non-max contract extension in the class of 2020. So far, Minnesota's Anthony Edwards, Charlotte's LaMelo Ball, Indiana's Tyrese Haliburton and Memphis' Desmond Bane have agreed to max extensions.
The Pistons drafted Stewart 16th overall out of Washington, where he had played for coach Mike Hopkins.