The 28-year-old, in his second season in the Cubs' farm system, was named the 2011 Pacific Coast League Most Valuable Player after batting .331 with an Iowa franchise-record 38 home runs and 109 RBIs in 129 games.
"What a year," Cubs manager Mike Quade said. "It's funny, when I look at the numbers, he's been doing this awhile. He's always put up big numbers in Triple-A, but I think this is a banner year for him."
LaHair spent the first seven years of his career bouncing around the Mariners' Minor League system after being drafted in the 39th round of the 2002 First-Year Player Draft. His first and only trip to the Majors was in 2008, when he batted .250 with three homers and 10 RBIs in 45 games.
"I'm just going to have fun," LaHair said. "I don't want to change too much. I just want to be myself and have fun with the guys. ... I'm just going to try to approach it the same way. I'm gonna try to hit balls hard, and whatever happens, happens."
The Cubs already have a veteran first baseman in Carlos Pena, but Quade said the team plans to play LaHair in the outfield as well as off the bench.
"He's played some outfield. We've asked him to do a little bit of that," Quade said. "So we'll give [Alfonso Soriano] a day sometimes. We'll mix and match."
Quade said LaHair would be the only callup until the Triple-A season ends on Monday.
"Right now, I think we are where we're at," he said. "We talked about some folks, but I think we're going to wait until the season ends in Iowa to make further decisions."