John R. Guerrant was born on July 12, 1865, in Callaway, located in Franklin County, Virginia. He and his brother Samuel "Cap" S. Guerrant, M.D., (July 12 1867-October 28, 1940), were orphaned at the age of ten and raised by their aunt (the sister of their mother), Mary (Saunders) Callaway, the wife of James Steptoe Callaway. Upon turning twenty-one, the Guerrant brothers inherited the family estate, "Algoma," which consisted of 5,000 acres near Callaway. Samuel Guerrant was a physician and horticulturalist at Algoma, and one of the most active civic leaders and Presbyterian churchmen in Franklin County until his death. John R. Guerrant graduated from Washington and Lee University and the School of Medicine at the University of Virginia. On July 12, 1892, Guerrant married Katherine Randolph Lee (born August 27, 1865), the daughter of Charles Carter Lee (1798-1871) and Lucy Penn Taylor (1827-1913) and had two daughters, Elizabeth and Marie. In 1906, Guerrant served a term in the Virginia House of Delegates in 1906.

John R. Guerrant died in Salt Lake City, Utah in 1930.