Apple’s chief operating officer plans to hand the role off this month and retire later this year after roughly a decade as the tech giant’s No. 2 under Chief Executive Tim Cook.

Mr. Williams was long considered a leading candidate to replace Tim Cook as the company’s next chief executive.

Apple has promoted Sabih Khan to chief operating officer, putting him in charge of the company’s supply chain when the tech giant and its peers are navigating Donald Trump’s trade war.