The company, which was bought from its founder by a management buy-in team led by Chris Lovell three years ago, was previously headquartered in Cardiff with no central London presence.
The new London headquarters are part of a restructuring of the company, which also sees Mike Leeson, the managing director of the Cardiff office, promoted to managing director, running Golley Slater's advertising interests nationally. The chief executive of the Birmingham agency, Ken Copson, takes over as the chairman of the advertising division.
Along with the structural overhaul, Golley Slater is launching a new positioning based around the strapline: "A return on Inspiration."
The company has agencies in nine cities around the UK and operates across a range of marketing services, including direct marketing, PR, digital, promotional marketing and executive search, as well as advertising. Its group clients include TK Maxx, Twinings, Mitsubishi and COI, and advertising billings are around £18 million out of total group billings of £90 million.
Lovell said the £2.5 million investment in a London headquarters was "a tipping point for Golley Slater".