At the onset of World War I he enlisted in the Canadian Expeditionary Force and served on the battlefields of France and Belgium.

Captain McNair served again during World War II as a member of the Royal Canadian Artillery Reserves.

Despite province wide protests, on April 27, 1950 McNair's government implemented a four percent provincial sales tax to help finance the public education system and social services.

McNair served as premier for twelve years until the defeat of his government in 1952 at which time he returned to the practise of law.

He was awarded a Rhodes Scholarship to attend Oxford University, where he further distinguished himself by earning first-class honours, and received a B.A.

Following the outbreak of the Second World War, McNair volunteered once again and served as a captain in the Royal Canadian Artillery Reserves.

In the Legislative Chambers, McNair distinguished himself as a gifted speaker and was widely regarded as the most able member of Dysart's government.

Dysart frequently suffered from ill-health and during his many absences from the Legislature McNair served as Acting premier.

Considered to have been New Brunswick's most intellectually gifted premier, McNair was also a shrewd politician and excellent debater who regularly used his cutting wit to fend off criticism from the Opposition benches.

Governing the province during the war years and through harsh economic times, McNair is credited with introducing a succession of budgetary surpluses, undertaking a massive rural electrification program, improving education in rural areas, expanding the role of the civil service, centralizing the provincial government offices and New Brunswick Electric Power Commission in Fredericton.

For the August 1944 general election, McNair became the first politician in Canada to employ the services of a professional advertising agency to direct a political campaign.

Not long after McNair assumed the premiership, his wife's health deteriorated in an alarming fashion and she spent much of her time in hospitals.

He was designated a Companion of the Order of Canada on July 6, 1967, but the award had to be presented posthumously as the scheduled ceremony did not take place until September 23, 1968.