Forster set up the eponymous agency after leaving the Body Shop, where she was communications director, in 1996. In 2003, she sold the majority of the agency, which she had previously owned outright, to staff.
A non-executive director of the agency for the past 18 months, Grounds is the former deputy chief executive and director of marketing and campaigns of animal charity the RSPCA. Before that, he was a senior executive at children's charity the NSPCC, including seven years as director of comms. He has also chaired charity PR body CharityComms since 2012.
Grounds chairs a board that now contains two new directors; innovation director Gillian Daines and director of client services George Ames. Both have been with the agency for several years.
Powell Smith said: "There’s real momentum building behind the desire for businesses to be deliver more social impact and last year we became a founding UK B Corp. I believe the new board will ensure that we can help even more organisations create meaningful value for themselves, their stakeholders and wider society."
B Corp status is a scheme originating in the US whereby companies agree to be audited for adherence to a number of environmental, social and other factors.
"I’ve spent my whole career working for organisations committed to social change and could not be more convinced that in these challenging times, Forster and its clients have a more crucial role to play than ever," Grounds said.
With around 25 staff, Forster clients include charities Anna Freud and Carers UK, shipping and logistics firm DP World, and potentially the UK Government, after it was named on a provisional Government Communication Services roster, to be confirmed later this month.