Walter G. McDonald was born on February 17, 1888, at Minnewaukan, North Dakota to Thomas M. and Agnes (Gardener) McDonald of Perth, Ontario. He was educated at the rural schools of Benson County, attended town schools at Minnewaukan, and completed his high school course in the preparatory department of Fargo College. In 1912, he received the A. B. degree at Fargo College. He studied law for one year at the University of Michigan and two years at the University of North Dakota, where he graduated with the LL. B degree in 1916.
He was admitted to the bar in July of that year and then began to practice at Minnewaukan, handling varied work of both civil and criminal cases. He had been retained as a counsel in many litigations of importance in Benson and surrounding counties. McDonald was elected state's attorney of Benson County in November 1920, and had been reelected at each successive two-year periods until 1934. He was also involved in the Oberon Lodge No. 62, Independent Order of Odd Fellows, Ancient Order of United Workmen, in addition to other groups.
McDonald married Claribel DuBois of Baraboo, Wisconsin, on February 14, 1921 in Fargo. He died in Mesa, Arizona, in April 1965.