George Mills Harris was born February 3, 1883, the son of George Wells Harris and Elizabeth Mills Harris. George M. grew up on the family farm in Wethersfield, Connecticut. Harris Hill Farm is known for its Brown Swiss herd, which his father, George W., was instrumental in introducing to the United States from Switzerland.

After graduating public high school in Hartford, George M. attended Yale University where he was on the track team for four years. Following graduation in 1905, he briefly returned to the farm in Wethersfield before spending 1906 working in New York City as an instructor and athletics coach, and then returning to Harris Hill Farm the following year. From 1918 to 1919 George M. attended the Coast Artillery Officers' Training School and was commissioned as a Captain. He also served as Assessor for the Town of Wethersfield from 1925-1949.

George M. married Beatrice Griswold and had one son, George Griswold Harris, in 1934. In 1942, when his father George W. died, George M. and his brother, Rodney Harris, took over the family farm on Prospect Street in Wethersfield. George M. set out to improve the Brown Swiss herd breeding program and to grow Harris Hill Farm. He purchased a young bull names Mandarin of Laurel Ridge, who was to become the sire of Harris Hill Mandarin's Mary, who earned her place on the National Honor Roll for milk.

When George M. Harris died in 1956, his son George G. took over operation of the farm, eventually buying out Rodney and moving the farm to New Milford, Connecticut. There George G. continued the excellent breeding program of Brown Swiss Cattle that his father and grandfather had begun before him.