Hudson Sandler, which is headquartered in London but also has offices in Moscow and Hong Kong and an affiliation with US agency KCSA, was acquired by Grayling, Citigate and Huntsworth Health owner Huntsworth in 2008.
Following a transaction last Friday that involved Hudson Sandler becoming a limited liability partnership (LLP), Huntsworth is now a minority shareholder in the business, rather than outright owner. Huntsworth's stake is believed to be around a quarter.
Hudson Sandler managing partner Andrew Hayes told PRWeek that the business had "always been independently managed", and that it would be business as usual in terms of servicing clients.
He said the move gave the firm the opportunity to give its 40 staff more ownership of the LLP. It was previously a limited company.
"It is the intention of the board to spread that partnership interest more broadly across the team, because we believe that partnership is important to developing the business and people's careers," he told PRWeek.
A Huntsworth spokeswoman said: "As part of the ongoing development of the Group, Huntsworth made the decision to restructure Hudson Sandler to give management a greater stake in the equity of the business. Huntsworth remains an active and supportive shareholder of Hudson Sandler."
Hayes, one of few senior PR agency leaders to publicly back the UK's withdrawal from the European Union, also said that the firm had seen a strong rise in activity in its consumer, Russian and financial services business in recent months.