Johnston took the job on an interim basis when Loewy founder and former CEO Charlie Hoult became vice-president (development) in May. He will now be in charge of the company on a permanent basis.
Johnston orginally joined Loewy in 2006 as non-executive director and was appointed chairman of Loewy's brand communications cluster of agencies in February.
In September, Loewy Group confirmed that it will move all of its PR agencies into one office, most likely a location in Soho, after months of speculation. The agencies will maintain their separate brands of BMA, Mantra PR, and Rainier PR.
Johnston has previously held senior posts at GB Group plc, Event Marketing Solutions and Alterian plc, which he co-founded and eventually floated in 2000.