US President Donald Trump has announced that General H. R. McMaster will be named national security advisor and Keith Kellogg will be chief of staff for the National Security Council.
Trump announced the pick on Monday at his Palm Beach club, Mar-a-Lago.
He said McMaster was "a man of tremendous talent and tremendous experience".
"He's a man of tremendous talent and tremendous experience. I watched and read a lot over the last two days, he is a highly respected by everybody in the military and we're very honored to have him."
The President had been looking for a replacement for Michael Flynn, who was ousted last week.
Trump asked for Flynn's resignation on February 13 after reports emerged the retired lieutenant-general had misled Vice-President Mike Pence about having spoken to Russia's ambassador about US sanctions before Trump's inauguration.
General McMaster said: "I would just like to say what a privilege it is to be able to continue serving our nation and I'm grateful to you for that opportunity.
"And I look forward to joining the National Security team and doing everything I can to advance and protect the interest of the American people."