Harris, 57, has had his current post since February 1999. Previously he had been senior vice president for communications at the Chrysler group.
Harris had considered retiring in 2002, but said last year he would stay at least through 2003.
Kowaleski, 51, joined GM as executive director of product communications in March 1999 and was named a regional vice president in 2002. He is a member of the GM North America Strategy Board.
Kowaleski will become a member of GM's Automotive Strategy Board and lead the global Communications Strategy Board. He will direct all of GM's corporate, product, brand and internal communications efforts around the world.
Before joining GM, Kowaleski served as director of communications strategy for DaimlerChrysler and vice president of marketing and communications for Chrysler Europe.