The Mariners, who were off Thursday, open a three-game series with the Phillies at Safeco Field on Friday.
Utility infielder Luis Rodriguez was optioned to Tacoma to open up a spot for Ackley, who will play second base for the Mariners. The move was announced after Wednesday night's 3-1 victory over the Angels.
"We just felt it was time," general manager Jack Zduriencik said. "We'd talked about some time in June we thought he'd be ready. In discussion with the coaches down there, they all felt this is the time. He's been swinging the bat well. So here it is. He'll be here Friday and we'll look forward to his contributions."
Ackley, the second overall pick in the '09 Draft, is expected to step in immediately at second base for a Mariners squad that is 35-34 despite ranking last in the American League in batting average and scoring.
"It's time to get him up here," manager Eric Wedge said. "He needed more experience at second base at the Triple-A level, but he's ready to be up here. I hate to option Luis Rodriguez out, but he does have options. I'm sure he'll be back. But Ackley is a guy we feel strong about. We like his bat and he's made tremendous strides at second base."
Ackley, 23, was hitting .303 with 57 runs scored, nine home runs and 35 RBIs with Tacoma. He also walked 55 times in 66 games and had a .421 on-base percentage.
Adam Kennedy had been getting the bulk of the playing time at second and leads the Mariners with a .275 batting average. He was taking ground balls at third base prior to Wednesday's game, and Wedge said he'd find ways to keep the veteran in the lineup.
"We're going to make it work," Wedge said. "When you talk about what we've had to do with regard to juggling the lineup and getting guys in there, we've made it work up to this point in time. We're still trying to find ourselves offensively, and we think Ackley will be part of that. We'll make sure Adam is getting his at-bats as well."
Zduriencik said Ackley has been playing well at second base, which was one of the reasons the Mariners had him spending time in Triple-A this season. He was an outfielder and first baseman at North Carolina before being converted to second after the Mariners drafted him.
"All the reports are that the progress has been very satisfying," Zduriencik said. "The game up here is quicker and faster and until you give a guy a chance up here, you hope it'll continue. So we'll see. But we're real happy with what he's done. So here's his time and we'll see how it all falls into place."
Ackley will be the ninth rookie to play for the Mariners this season. Two of them played big roles in Wednesday's victory, with Carlos Peguero hitting the game-winning two-run single and Greg Halman blasting his first home run.
Rookie pitcher Michael Pineda, who will start Friday night against the Phillies, has also been a big factor in the team's surprising start.
"Obviously we've got a lot of young guys who have contributed," Zduriencik said. "Tonight is a good example. We expect Dustin to come up and fall into place and contribute as well.
"We know his personality and the kind of guy he is. He'll fit in well with this group. It's nice what's going on and we'll continue this as we're doing right now. When guys earn the right to be up here, they'll be here. And we think right now, he's earned that right."