Born into the Mormon community at Safford, Arizona, Ellsworth spent the earliest years of his life in Payson, Utah, where his father, James, managed a bank, and later served a term as mayor. In 1924, the family moved to Salt Lake City, then to Ogden, before relocating to Long Beach, California. George spent much of his youth moving from one part of the country to another, graduating from Central High School in Kansas City, Missouri, in 1934. After attending junior college for two years, he embarked to the north central states for an LDS Church mission. Following his mission, George returned to Utah, where he registered for classes at the Utah State Agricultural College (USU) in Logan.

As Ellsworth pursued his nascent interest in history, he found particularly rewarding those classes taught by Joel E. Ricks, J. Duncan Brite and Milton R. Merrill. After his graduation, Ellsworth accepted a position as principal of Virgin Valley High School in the remote Mormon community of Bunkerville, Nevada. While in Nevada, he met and married Maria Smith of Snowflake, Arizona. Shortly after their marriage, George enlisted for service during World War II, where he served as a clerk, and later as chaplain, with the Army Air Corps.

Partially as a result of his Mormon upbringing, which emphasized the blessings of hard work, but also from his impoverished college and military years, Ellsworth developed an indefatigable capacity for work. Following release from the military in 1946, he entered the graduate program at UC Berkeley, and in little more than four years, completed requirements for both the masters and doctoral degrees.

Ellsworth's conscientious work ethic served him well once he joined Joel Ricks and Duncan Brite as the junior member of USU's History Department in 1951. One of his primary responsibilities was to develop a course specifically on Utah, where he pioneered the use of a wide range of primary documents to study the State's past.

USU hails George Ellsworth as its first archivist. Being both a keeper as well as a user of primary documents made George's approach to Utah history unique. Ellsworth's collection of documents enabled him to visualize the panorama of history, or to focus on the smallest details of an event, and to always discover the connection between the two. Ellsworth knew the sources, and was frequently critical of students and professionals who failed to consider them in their writing. An advocate for balance and impartiality, Ellsworth also encouraged the study of history from all angles.