Parmelee, 24, put up some of the best numbers in Triple-A this year, batting .338/.457/.645 with 17 homers, 17 doubles and 49 RBIs in 64 games with the Red Wings.
However, Parmelee didn't fare as well in three previous stints with the Twins this season, batting .204/.283/.324 with two homers and six RBIs in 40 games. He was impressive as a September callup last season, when he hit .355 with four homers and 14 RBIs in 21 games.
Parmelee, who is expected to see time at first base and in right field, started in right and hit seventh in Wednesday's game against the Mariners.
"You're going to see him moving around. Here [right field], left field, first base, DH, whatever we have to do. Get him some at-bats, get some guys breaks," Twins manager Ron Gardenhire said. "I'll try to get his bat in there as much as I can. We'll use everybody. It will give me an opportunity to give a couple other guys some breaks."
Gray, meanwhile, posted a 5.71 ERA with 26 strikeouts and 22 walks in 52 innings with the Twins. Since he was outrighted to Triple-A, he has been taken off the 40-man roster.
With the move, the Twins went back to carrying 12 pitchers and 13 position players. They now have 36 players on the 40-man roster.