Born in Philadelphia, McMaster graduated from the United States Military Academy in 1984 and earned a Ph.D. in American history from the University of North Carolina at Chapel Hill in 1996.

[4][5] McMaster resigned as National Security Advisor on March 22, 2018, effective April 9,[6][7][8] and accepted an academic appointment at the Hoover Institution, Stanford University, in 2018.

[19] It harshly criticized high-ranking officers of the era, arguing that they inadequately challenged Secretary of Defense Robert McNamara and President Lyndon B. Johnson on their Vietnam strategy.

In 1989, he was assigned to the 2nd Armored Cavalry Regiment at Warner Barracks in Bamberg, Germany, where he served until 1992, including deployment to Operation Desert Storm.

Shortly after McMaster took command the regiment deployed for its second tour in Iraq and was assigned the mission of securing the city of Tal Afar.

President George W. Bush praised this success, and the PBS show Frontline broadcast a documentary in February 2006 featuring interviews with McMaster.

McMaster deployed his soldiers into Tal Afar on a permanent basis, and once the local population grew confident that they weren't going to withdraw nightly, the citizens began providing information on the insurgents, enabling US forces to target and defeat them.

[29] McMaster passed command of the 3rd ACR on June 29, 2006, and joined the International Institute for Strategic Studies in London, as a Senior Research Associate tasked to "conduct research to identify opportunities for improved multi-national cooperation and political-military integration in the areas of counterinsurgency, counter-terrorism, and state building", and to devise "better tactics to battle terrorism.

"[32][33][34][35] Though the Army's rationale for whether a given officer is selected is not made public, McMaster's initial non-selection attracted considerable media attention.

[36][37][38] In late 2007, Secretary of the Army Pete Geren requested that Petraeus return from Iraq to take charge of the promotion board as a way to ensure that the best performers in combat received every consideration for advancement, resulting in McMaster's selection along with other colonels who had been identified as innovative thinkers.

[41] In July 2010 he was selected to be the J-5, Deputy to the Commander for Planning, at ISAF (International Security Assistance Forces) Headquarters in Kabul, Afghanistan.

McMaster was nominated for major general on January 23, 2012, and selected to be the commander of the Army's Maneuver Center of Excellence at Fort Benning.

He was hailed as "the architect of the future U.S. Army" in the accompanying piece written by retired Lt. Gen. David Barno, who commanded U.S. and allied forces in Afghanistan from 2003 to 2005.

"[46] Barno also wrote, "Recently tapped for his third star, H. R. is also the rarest of soldiers—one who has repeatedly bucked the system and survived to join its senior ranks.

"[47] McMaster requested his retirement from the Army following his March 22, 2018, resignation as President Trump's National Security Adviser,[48] asking that he leave the service "this summer.

[57] In early August, McMaster was targeted by what some deemed a "smear campaign" after he fired several National Security Council staff members.

White House Press Secretary Sarah Huckabee Sanders denied the reports in a tweet, claiming nothing had changed at the National Security Council.

[6] McMaster's ousting closely followed the departures of several other high-ranking officials in the administration, including Trump's longtime assistant and communications director Hope Hicks, national economic advisor Gary Cohn, and Secretary of State Rex Tillerson.

[75] In September 2018, McMaster began work as a Bernard and Susan Liautaud Visiting Fellow at Stanford University's Freeman Spogli Institute for International Studies.

[79] In 2020, McMaster became a board member of Zoom Video Communications,[80] and advisor to Mischler Financial Group Inc.[81] He is Chairman of Ergo's Flashpoints Forum, a consultancy firm.

[83] In January 2022, he joined the advisory board of Strider Technologies,[84] a software firm focused on economic statecraft risk vis-à-vis strategic competition with China.

[89] White House press secretary Jen Psaki said that the Biden administration "was seeking to ensure that board members were 'qualified to serve' and aligned with the president's values.

[91] He was interviewed by Anderson Cooper at length especially about the history of Trump's decision to settle a deal with the Taliban and exclude the government of the Islamic Republic of Afghanistan from the negotiations.

Naval Institute Board of Directors, who said it was "... a sober, thoughtful, intelligent volume that deserves shelf space for anyone serious about U.S. foreign policy in the first part of the 21st century.

"[95] McMaster is the author of Dereliction of Duty: Lyndon Johnson, Robert McNamara, the Joint Chiefs of Staff and the Lies that Led to Vietnam and has co-authored several other books on foreign policy.