US President Donald Trump has chosen army Lt Gen HR McMaster as his new national security adviser.
Mr Trump announced the choice on Monday at his Palm Beach club, Mar-a-Lago.
He said Lt Gen McMaster is "a man of tremendous talent and tremendous experience".
Mr Trump said retired army Lt Gen Keith Kellogg, who had been his acting adviser, will now serve as the National Security Council chief of staff.
The president had been looking for a replacement for retired general Michael Flynn, who was ousted last week.
Mr Trump also said he would be asking John Bolton, a former US ambassador to the United Nations, to work with them in a "somewhat different capacity".
He made the announcement from a luxurious living room, sitting on a settee between Lt Gen McMaster and Lt Gen Kellogg.
Mr Trump brought four options for the position to Mar-a-Lago over the weekend for in-person interviews, Lt Gen McMaster among them.
Lt Gen McMaster called the appointment a "privilege".
The president told reporters as he exited the room that Vice President Mike Pence had been involved in the process.
The position of national security adviser does not require senate confirmation.
Mr Trump pushed out Mr Flynn a week ago after revelations that the adviser had misled Mr Pence about discussing sanctions with Russia's ambassador to the US during the presidential transition.
The president said in a news conference on Thursday that he was disappointed by how Mr Flynn had treated Mr Pence, but did not believe Mr Flynn had done anything wrong by having the conversations.
Mr Trump's first choice to replace Mr Flynn, retired vice admiral Robert Harward, turned down the offer.