The Suns fell to the worst mark in the Western Conference in 2012-13 after also failing to make the playoff in Blanks' two previous years as GM.
"Lance has been a trusted friend and colleague," Suns President of Basketball Operations Lon Babby said. "I thank him personally and professionally for his hard work on behalf of the Suns. We will continue to prepare for the offseason even as we look for his replacement."
The Suns went 98-132 overall under Blanks, who came to Phoenix after five seasons as assistant general manager in Cleveland.