Liddell, who came to GM from Microsoft 14 months ago, had been expected to be chosen to replace Chief Executive Officer Ed Whitacre Jr., but GM instead picked Dan Akerson to take over, The Detroit News reported.
A source close to the action said Liddell's departure was "amicable," but expected now that Akerson was "not giving up his job anytime soon."
Ammann said GM, which went through a quick bankruptcy proceeding in 2009, has "made great strides this last year in setting the financial strategy for the company."
"Chris and I have worked together very closely during this time, and I am committed to a seamless transition and to building on what we started," he said.
Liddell said, "I came to General Motors to be part of something great. My objective was to help rebuild this iconic company and I am particularly pleased that through this process, we have also developed a strong successor in Dan Ammann," the Detroit Free Press reported.
Liddell is credited with steering the company from its bankruptcy to its initial public offering with a strategy of creating a water tight balance sheet. Before its bankruptcy, GM was known to have difficulty identifying how much cash it had on hand, the News said.
GM completed 2010 with a profit of $4.7 billion. In its end of year statement, the company said, "material weakness regarding the financial reporting process no longer exists as of Dec. 31, 2010."
GM said Liddell would depart April 1, after helping Ammann transition to his new post.