An all-star the past three seasons, Walker was invited to Big League Spring Training this past January after hitting .292 in 131 games for Double-A West Tennessee in 2006.
He will join Iowa in time for the team's game against Memphis Saturday.
"This is really the first time I've been promoted in the middle of a season," Walker noted after hearing the news. "It's a new challenge."
A 2002 sixth-round Cubs draft pick from Georgia Southern, Walker entered 2007 a career .275 hitter in five minor league seasons.
Earlier Friday, the Smokies announced that RHP Billy Petrick had joined the team following a promotion from Class A Daytona.