"This is purely a personal decision on my part," Butler, 49, wrote in an e-mail message to Automotive News. "The company encouraged me to stay, but I need to take a step back and focus on the right priorities in my life. It's just time for a change in my path."
Butler was promoted in April to his current post as vice president of global strategic development, a newly created position to spearhead the brand's overseas growth strategy. His job was to drive "the next phase of Cadillac growth internationally," GM said at the time.
Two sources said Butler's decision came as a surprise to top GM executives. Butler reported to Bob Ferguson, vice president of global Cadillac, and was recruited by GM North America President Mark Reuss in 2010 to become the brand's top marketer.
"He's poured his heart and soul into Cadillac for three full years," said GM spokesman Dave Caldwell. Caldwell gave no time frame for naming a replacement.
Through July, Cadillac's U.S. sales are up 30 percent. The brand plans to introduce 10 new or redesigned vehicles by mid-2015 and wants to more than triple its sales in China by that year, to 100,000 units. GM also wants to jump-start Cadillac in Europe, where sales have long sputtered.
Butler, who joined GM as a co-op student in 1981, has been one of Cadillac's highest-profile executives during the brand's comeback in the wake of GM's 2009 bankruptcy.
He was Cadillac's top marketing executive from March 2010 to April 2013. He also served in marketing jobs at Pontiac, Chevrolet and OnStar, and he ran GM Egypt from 2005 to 2007.
Butler left GM once before, in 2009, to take a job at a telematics startup in Seattle. A chance encounter with Reuss at the Detroit airport led to an offer for Butler to return to the company as Cadillac's marketing chief.
Last month, GM lost another top Cadillac executive: Chase Hawkins, vice president of U.S. sales and service, who was dismissed July 19 for violating company policy, GM said.