The high-profile head of Cruise, General Motors’ autonomous-driving unit, is leaving the company, the carmaker said Thursday.

The executive, Dan Ammann, a former investment banker who is from New Zealand, gave up his job as G.M.’s president to take over Cruise at the beginning of 2019. Since then, expectations for autonomous driving have cooled as the magnitude of the technical challenge has become clear and as serious accidents have highlighted the risks.

Although G.M. did not provide an explanation for Mr. Ammann’s unexpected departure, the terseness of the company’s statement — lacking even perfunctory praise for his work — hinted at tension between him and top management.