He was born in England at the Moravian community at Fulneck in Yorkshire and, at the age of 7, sent away to the Moravian School at Niesky in Silesia on the borders of Saxony and Poland. After a continental Grand Tour he returned to England in 1784 and entered apprenticeship to John Smeaton the engineer (of Eddystone Lighthouse fame), and later, the eminent architect C.R. Cockerell. In the early 1790s he entered private practice and Hammerwood Park (link below) near East Grinstead in Sussex was his first independent work in 1792. In 1793 Ashdown House was built nearby. Both houses still stand. In 1795 he emigrated to America where he soon achieved eminence as the first professional architect working in the country.
As an engineer, he was responsible for the water supply to Philadelphia and, with his son, New Orleans, where he died. Of his many architectural triumphs, in addition to the Capitol, Baltimore Cathedral, The Pope House (Lexington, Kentucky), Chillicothe (Ohio), St John's Church and Decatur House (Washington), together with the Porticos of the White House still survive.
Principally, he was responsible for setting public architecture in the United States in the Greek Revival style. He complained in jest that after building just the Philadelphia Waterworks and the Bank of Pennsylvania, the whole town copied him, and his influence on public architecture endures.