President Donald Trump, right, shakes hands with Army Lt. Gen. H.R. McMaster, left, at Trump's Mar-a-Lago estate. AP President Donald Trump has announced that Army Lt. Gen. H.R. McMaster will be the new national security advisor.

McMaster replaces Michael Flynn, who resigned one week following reports that he discussed sanctions on Russia with the country's ambassador to the US.

Trump called McMaster "a man of tremendous talent and tremendous experience" as he made the announcement Monday afternoon at his Mar-a-Lago estate in Florida.

"I would just like to say what a privilege it is to be able to continue serving our nation. I'm grateful to you for that opportunity, and I look forward to joining the national security team and doing everything that I can to advance and protect the interests of the American people," McMaster said.

The New York Times reported that McMaster "is seen as one of the Army’s leading intellectuals, first making a name for himself with a searing critique of the Joint Chiefs of Staff for their performance during the Vietnam War and later criticizing the way President George W. Bush’s administration went to war in Iraq."

Trump also named Keith Kellogg, who had been the acting national security adviser, as the National Security Council's chief of staff.

Finding a new national security adviser has not been easy for Trump.

Retired Adm. Robert Harward was offered the role, but reportedly turned it down after seeing Trump's exhaustive 77-minute press conference last Thursday and the turmoil roiling the early days of the administration.

Harward also reportedly had concerns about the staffing on the NSC, including the appointment of White House chief strategist Steve Bannon.

"Harward wanted to undo the fairly large changes the president had made to the NSC that had inserted Bannon into the process," MSNBC host Chris Hayes reported. "The White House did not offer Harward sufficient assurances that he would have such autonomy."

Another candidate, Gen. David Petraeus, also reportedly withdrew himself from consideration over concerns about staffing within the NSC, according to The Wall Street Journal.