William Welch Deloitte established an accounting practice in London at age 25 and quickly proved to be an innovator. He helped develop a system that formed the basis for the English railway accounts, as well as a system of hotel accounting that became standard in the field.

Deloitte's reputation was so strong that he was asked to help unravel the infamous frauds at the Great Northern Railway and the Great Eastern Steamship Company. His importance to the accounting profession was recognized in 1889 when he was elected president of the Institute of Chartered Accountants. Deloitte was also a founder-member of the Chartered Accountants Benevolent Association.