Eric P. Kelly was born on March 16, 1884, in Amesbury, Massachusetts, attended his hometown high school and then Dartmouth College, from which he graduated in 1906. He then spent what he later described as "ten colorless, uneventful, and discouraging years" working for various Massachusetts newspapers. He also wrote short stories, two of which were finally published in 1916, ten years after his graduation from college.
By the end of World War I, in 1918, Kelly was in charge of the Foyer de Soldat (the French YMCA) at Quentin, France, where his duties included working with Polish soldiers in nearby regimental schools and supplying them with entertainment, athletics, and a canteen—a place they could relax, play cards, talk, and eat. Two years later, during the war between the Poles and Russian-backed Bolshevik forces determined to carry Russia's recent Communist Revolution into Poland (a war the Poles eventually won), Kelly was in Poland, serving in a traveling canteen near the front lines along the Bug River east of Warsaw. While there, he convinced the head chaplain of the Polish Army that the YMCA could do much good, and Kelly is credited with the organization's subsequent success in Poland.
In 1921, after the war, Kelly returned to Dartmouth College as an English instructor. He became a professor of journalism in 1929; and continue to teach until his retirement at age seventy, in 1954. During the 1920s, his interest in Poland continued to grow. In 1925- 1926, he worked as a lecturer in American literature and institutions at the ancient University at Krakow in Poland. From that time on, as Kelly himself said, he exercised himself in every way he knew "to aid the cause of Poland in the modern world." He lectured on Poland in schools, colleges, and libraries from Maine to California. He wrote innumerable articles and books about the Poles and their history— many of them for young readers. The most famous of these, The Trumpeter of Krakow, won the Newbery Medal in 1929.
During World War II, Kelly again contributed to the Polish cause by working through the U.S. State Department in Leon, Mexico, where he helped care for fifteen hundred Polish refugees. He was much honored for his work on Poland's behalf, receiving an honorary degree from the University of Krakow, the Polish Gold Cross of Merit, and the Pilsudski Medal. Kelly died on January 3, 1960.