He graduated from Harrisburg Technical School (Pennsylvania) in 1907 and married Grace Mildred Wrigley on November 5, 1915, with whom he had two sons: William Bell Clark, Jr., and Donald Wrigley Clark.
Although his first book was on military history, his work with the Pennsylvania War Commission from 1919 sparked his initial interest in naval affairs.
In the process of this research and writing, Clark developed a deep knowledge of the archival resources for this general period in naval history and made numerous careful transcripts of documents.
With the advice of the Secretary of the Navy's advisory sub-committee on naval history, Clark was appointed the first editor of the U.S. Navy's multi-volume documentary series on Naval Documents of the American Revolution, assisted by Morgan and his staff in the Early History Branch.
A Republican and a Presbyterian, Clark was also a member of the Naval Historical Foundation, the Historical Society of Pennsylvania, the Pennsylvania Genealogical Society, and served as vice president of the Illinois chapter of the Sons of the American Revolution.