The firm has recently seen a period of extensive growth with clients including the Welsh Assembly, Welsh Water, Welsh Health Estates and the Environment Agency Wales.
To cope with increased business, former head of housing at Vale of Glamorgan Council Ian Walters joins to head up the affordable housing team in Wales.
Kevin Ray will be working as a senior project manager working in both the public and private sectors and joins the firm from the Welsh Assembly Government, where he acted as a Professional Advisor for seven years.
And Michael Petersen arrives as a senior project manager concentrating on retail and residential markets. Mr Peterson will be working on the Newport Friars Walk scheme with Modus.
The firm has also appointed Alex McDonald as a senior consultant and has previously worked for CPC, Hornagold and Hills and the BBC.
EC Harris is based in Cardiff and now employs more than 50 people in the Principality.