Interstate Architects Limited has its origins in an architectural practice established by William Harvey Watkins in Bristol, England in 1900. The historic firm was involved in design of domestic, commercial and health buildings in the southwest of England.
In 1952 the firm of W. H. Watkins Gray & Partners was commissioned to design a Teaching Hospital for Nigeria in Ibadan. As a result, an office was set up in Lagos, with work expanding to such an extent that a new independent partnership was created under the name of W. H. Watkins Gray Nigeria
The firm would later be incorporated as a Limited Liability Company in 1987, becoming known as Interstate Architects Ltd (IAL). The Company has accredited members of the NIA and registered members of ARCON.