Jason Miller, who was named as White House communications director by President-elect Donald J. Trump two days ago, has informed Mr. Trump that he will not take the job, according to a statement from Mr. Miller.

In the statement, Mr. Miller said he wanted to spend more time with his family. His wife is expecting their second child in January, he said.

“It’s clear they need to be my top priority right now, and this is not the time to start a new job as demanding as White House communications director,” Mr. Miller wrote.

A veteran of several Republican campaigns, Mr. Miller was an avid supporter of Mr. Trump, appearing regularly on television on his behalf throughout the campaign. He had been a principal spokesman during the transition period.