Erwin Stanley Bradley was born on March 20, 1906, in the small town of Fairview in Huntingdon County. He is the only son of William and Ida Bradley; he had three sisters. Bradley's father died when young Erwin was only three-years-old, leaving the family reliant on Ida Bradley's seamstress skills and the price brought from selling surplus milk. Though their poverty would ease in 1914 when Ida Bradley remarried, Erwin Bradley needed to help support the family by working in the mines. Graduating from Dudley High School in 1924, he worked his way through the teaching certificate program at Shippensburg Normal School (now University) and then earned a B.A. in mathematics from Juniata College in 1930.

Bradley taught at a number of schools throughout Pennsylvania. Eventually, he earned his M.A. from the University of Michigan at Ann Arbor, taking summer classes to earn credits. In 1940, he moved to Mississippi, taking a position at the Jefferson Military College, a post he would hold until drafted in 1942. He served in the United States Army as a radar repair officer until October 1945, when he was discharged and returned to Mississippi and Vivian, his wife since 1941. He stayed at Jefferson until 1947 when he received an appointment to Union College in Kentucky. During his early years there, he undertook a doctor program in History at the Pennsylvania State University. His dissertation was entitled "Post-Bellum-Politics in Pennsylvania."

In his new position at Union College, Bradley was appointed to write a history of the school in time for its 75th anniversary. This book would be augmented and republished for the 100th anniversary of the school in 1979. In addition to contributing articles to a number of journals, Bradley would write two full book length studies of Pennsylvania politics of the Civil War era. The first of these was The Triumph of Militant Republicanism in 1964, a survey of Pennsylvania politics of the Civil War and Reconstruction period. Reviewer Richard O. Curry wrote in Pennsylvania History, that while the book did not contain much new material, it would be useful as a "background for scholars who would probe further and deeper." The second book was 1966's Simon Cameron: Lincoln's Secretary of War. This study aimed at rehabilitating the reputation of Simon Cameron, known largely for corruption. Reviewer Fred Nicklason wrote in Pennsylvania History that "Bradley's attempt to refurbish Cameron's reputation is not convincing," taking him particularly to task for his research methodology. Bradley also served as the Curator of the Lincoln Library Collection at Union College. He rose through the administrative ranks to chair the History and Political Science Departments, as well as the Chairman of the Division of Social Studies. Bradley retired in 1974.

Dr. Erwin Bradley passed away in Chambersburg, Pennsylvania on June 10, 2009. Union College currently commemorates Bradley's service with the "Dr. Erwin S. Bradley History Award," given to the student with the highest grades in history courses in the college.