Jones joins in a part-time, non-executive capacity, to advise on business development matters.
The top-level changes have also led to Gay Collins, one of Penrose's four founding partners, taking on the role of managing director.
The three other founders have also taken on specific roles within the agency, with Andrew Nicholls handling marketing, PR and new business, Shona Prendergast handling human resources and Louise Hatch covering client services.
Collins said the changes have been made in a bid to increase the size of the agency.
'We have been going for almost five years and have grown in that time.
We want to take that to the next stage and go from a small company to a medium sized one. Bill's experience with Lexis will be invaluable in achieving that,' she said.
She added that this development did not include the agency changing focus away from capital markets and financial services.
Jones stood down as CEO of Lexis PR this year after an MBO by the agency's other directors (PRWeek, 19 April).