WASHINGTON — The Pentagon press secretary, John F. Kirby, the voluble public face of the Defense Department for the past year and a half, is moving to the White House in a new role as President Biden’s national security voice, the White House announced on Friday.

Mr. Kirby will work alongside the new White House press secretary, Karine Jean-Pierre, who started in her position on Monday, administration officials said. He will serve as the National Security Council’s coordinator for strategic communications and will report directly to Jake Sullivan, Mr. Biden’s national security adviser.

“John understands the complexities of U.S. foreign and defense policy, and he will ably represent the administration on important national security issues,” Mr. Biden said in a statement on Friday. The White House said Mr. Kirby will coordinate efforts to “explain United States policy and will serve as a senior administration voice on related matters, including as appropriate at the White House podium.”

Mr. Kirby is a veteran government public affairs officer and has long been a respected figure at the Pentagon. A retired Navy rear admiral, he jumped from the Pentagon to the State Department in 2015 and worked closely with John F. Kerry, then the secretary of state, during the Iran nuclear negotiations and for the last two years of the Obama administration.

More recently, Mr. Kirby has worked closely with Defense Secretary Lloyd J. Austin III, holding multiple briefings each week as he has narrated Russia’s ongoing war in Ukraine and the American response.

During the Obama administration, Mr. Kirby spent a year as the Pentagon spokesman under Defense Secretary Chuck Hagel, and he has been the spokesman for the Navy as well. He was commissioned in the Navy in 1986 and served for nearly three decades. He retired at the rank of rear admiral in 2015.

It is unusual for a former military officer to take such a senior role on the White House’s communications team, but administration officials said Mr. Biden admired Mr. Kirby’s ability to explain American national security policy to the public.

“I am very grateful to President Biden for his confidence in me and to Secretary Austin for his tremendous support and leadership these last 18 months,” Mr. Kirby said in a statement.