Rex W. Tillerson, the president and chief executive of Exxon Mobil, has emerged as President-elect Donald J. Trump’s top choice to become secretary of state, according to a person with direct knowledge of the search process.

The news is the latest turn in what has become the most extended drama of Mr. Trump’s transition effort, with a rotating cast of seeming front-runners to become America’s top diplomat. Choosing Mr. Tillerson would add to a long list of wealthy businesspeople in high-ranking Trump administration posts.

As Exxon’s top official, Mr. Tillerson has extensive experience working with foreign leaders. Some of his foreign relationships, especially those with Russia, could come under particular scrutiny during a Senate confirmation hearing.