"After spending three years doing it, I've simply decided that I want to spend more time at home in Texas," Moreland said in his note.
Moreland, who played for the Cubs from 1982-87, joined play-by-play broadcaster Pat Hughes for the 2011 season, replacing popular Ron Santo, who was in the booth from 1990-2010. Santo died in December 2010.
Moreland, 59, known as "Zonk," played 12 seasons with the Phillies, Cubs, Padres, Tigers and Orioles, and he won a World Series in 1980 with Philadelphia.
"He was fun to be around, insightful and a team player," Hughes said of Moreland in a statement. "Like our listeners, I feel like I learned a little more about baseball each day from him. I wish Keith all the best, and I will miss him greatly."
After his playing career ended, Moreland spent 16 seasons as the University of Texas baseball color analyst and nine seasons as the Longhorns' football color analyst.
Carrie Muskat is a reporter for MLB.com. She writes a blog, Muskat Ramblings, and you can follow her on Twitter @CarrieMuskat. This story was not subject to the approval of Major League Baseball or its clubs.