In association with a few friends, he formed the Salisbury Real Estate Company that bought the Welmoed East Farm and developed in the early 1930s into the beginning of North Eastern suburb of Highlands. The project proved to be very viable, and D'Arcy Cathcart was able to make his mark architecturally. While most of the houses followed the English pattern, his own house 'Chaninga' nestled on a prominent kopje in the suburb, and 'Limbe Lodge' (now the public Services Training Center) stood out markedly.

In reviewing D'Arcy Cathcart's style Peter Jackson wrote that his neo-classical approach "was a based more on early English Georgian architecture…His successful design of N.E.M. Building, and Town house competition design became 'vary fashionable' throughout the 1930s-1940s for municipal and government buildings. His practice was to later open offices in Mutare, Bulawayo, Ndola and Lusaka (Zambia) and D'Arcy Cathcart himself retired in 1956, but returned to practice as a consultant from 1964 until his dead six years later.

A founder member of the Institute of Southern Rhodesian Architects (now Institute of Architects Zimbabwe) he presided over the organization from 1929-30 (succeeded Cope-Christie) and again from 1944-46.