Colen Campbell began his career in the late-17th century as a lawyer, but later turned architectural publicist as compiler of Vitruvius Britannicus volumes I to III (1715-1725), and then architect, in the early-18th century.
Further reading:
Colvin, Howard, A Biographical Dictionary of British Architects: 1600-1840, 3rd edition (New Haven and London: Yale University Press, 1995), pp. 209-213.