The new venture, Williams Nicolson, is billed as a "strategic communications and change management consultancy" focused on "data-led communications".
The firm's six launch clients include international recruitment business Robert Walters, AIM-listed professional services group Ince, Japanese insurance company Sompo, and HeliOffshore, the European organisation for the offshore helicopter industry.
Williams, the Capital MSL founder who headed Portland's financial comms division before departing late last year, worked briefly with Nicolson when he was chief executive of Porta and she was a partner at Porta-owned agency Newgate.
Nicolson earlier founded and led two PR agencies: Comtext Communications and Bread, selling the latter to 3x1 Group in 2015. She is the author of 'The Entrepreneurial Myth: A Manifesto for Real Business', published in 2018.
Williams explained the approach of the agency: "It's very much driven by what clients want, to suit the way the world works, with big data as part of that. That applies to every part of what we do.
"We are describing ourselves by scenario rather than line of business. If your client is going in to acquire a company, there are multiple stakeholders that might be relevant, from the government to the man on the street and everybody in between, and there are multiple channels. Our view is, to help you navigate your way through this kind of situation, you want somebody alongside you to help you think through what the issues are, what the opportunities are, and to help you put together the level of support for the right places that you need."
The agency launches with a team of six, each of whom has equity in the business. "It's an old-fashioned City partnership-type set up, I suppose," said Williams, who is also a former partner at Finsbury and ex-PRCA chairman.
He said the business is "never going to be huge: 30 to 50 people maximum" and would focus on senior staff with few clients. "Each partner will have a relatively small number of clients to provide that high level of support," he added.
Williams Nicolson is based at The Tea Building, which is home to Shoreditch House in the East London district. Williams said: "We are set up for a new era and designed for flexible working, but we still believe a physical office is an important place to occasionally congregate. We want somewhere for unplanned discussions and meaningful collaborations.
"We don't want people to come to the office to look at emails, but we do think it's a good idea to get people together to work creatively and to socialise."