But how will that forthright demeanor translate in the Trump administration?
The president places a high value on loyalty and some experts are already questioning whether Trump will actually listen to McMaster.
Max Boot, a military historian at the Council on Foreign Relations, was skeptical that McMaster would be able to bluntly shoot down ideas from the president.
"Or do you have to sugarcoat it and handle him with kid gloves?" he told the New York Times. "I suspect it’s the latter, and that’s not been H.R.’s approach. We’ll see if Trump is man enough to take it."
McMaster, who grew up in Roxborough and graduated from Valley Forge Military Academy and College, is known as an intellectual strategist. He earned a doctorate from the University of North Carolina, writing a dissertation that turned into Dereliction of Duty: Lyndon Johnson, Robert McNamara, the Joint Chiefs of Staff, and the Lies That Led to Vietnam, a seminal book on leadership and war gone wrong.
McMaster concluded that military leaders did not adequately confront the president with their objections.
That's a challenge he now faces himself.
One of the key tasks for the new national security adviser, Phillip Carter, director of the veterans research program at the Center for a New American Security, writes for the Washington Post, is that he "must build an ecosystem that enables and encourages generals to speak up — and dissent when necessary and appropriate."
Carter, a former Army officer notes: "This may be his greatest challenge, because of the president’s thin skin. Trump has shown a predilection for lashing out against dissenters [...]."
Some experts have said they believe McMaster will be up to the task, and the Trump administration knew – or should have known – what it was getting when the lieutenant general was brought on board.
"There’s no question that the current White House team will be a tough group to break into, but if they expect H.R. McMaster to pull his punches as national security adviser, or sit in the background passively amidst the infighting, they have hired the wrong guy," Joseph Collins, director of the Center for Complex Operations at National Defense University, told Politico.
In his first week on the job, McMaster showed an early willingness to break from Trump. At a National Security Council meeting, he reportedly said the term "radical Islamic terrorism" – a phrase the president uses – should be avoided.
McMaster, who most recently had been the director of the Army Capabilities Integration Center, was named to the NSA post last week in the wake of Michael Flynn's ouster. Flynn was forced out after it became public that he had misled Vice President Pence about having spoken with the Russian ambassador about sanctions.
Another candidate, retired Vice Adm. Robert Harward, reportedly turned down the job because he was not confident he would be able to select his own staff and have enough autonomy.