Charles Firth was a British historian best known for his studies of Oliver Cromwell, the English Civil War, and the Commonwealth. Writing more fully as Charles Harding Firth, he combined close attention to documentary evidence with an interest in the people behind political events. His Oliver Cromwell and the Rule of the Puritans in England offers an accessible introduction to a turbulent period.

Educated at Clifton College and Balliol College, Oxford, Firth built his career as a teacher, editor, and researcher. He became Oxford's Regius Professor of Modern History and worked to encourage students to study original sources. His scholarship drew on letters, memoirs, official papers, and military records rather than relying solely on inherited accounts of the past.

Among his other important works are Cromwell's Army and The Last Years of the Protectorate. He also edited historical documents, including the Clarke Papers, helping later researchers examine the evidence for themselves. Firth's contribution lies in connecting institutions and military organization with individual choices and political convictions. His books remain part of the scholarly foundation for understanding seventeenth-century England.