Mr. Grenell, whose outspokenness throughout his career as a political operative and then as ambassador has prompted criticism, is a vocal Trump loyalist who will lead a group of national security agencies often viewed skeptically by the White House.

He would take over from Joseph Maguire, who has served as the acting director of national intelligence since the resignation last summer of Dan Coats, a former Republican senator from Indiana. Mr. Grenell, who has pushed to advance gay rights in his current post, would apparently also be the first openly gay cabinet member.