Weber’s EMEA chief Colin Byrne told PRWeek that Prime’s reputation for creative digital innovation was a key factor in deviating from Weber’s preferred approach of growing organically.
Financial terms have not been disclosed but Prime is understood to have made fee income of $30m last year.
"It’s a chunk of change, but this is not just a revenue play," said Byrne. "Prime has been one of the most creative and award-winning agencies in the world and has a reputation for creative digital innovation.
"This isn’t just about acquiring a Swedish firm for another dot on the map. Often a big agency gobbles up a smaller one and expects them to change to their way of working. This is a partnership and we have a lot to learn from them."
The deal was two years in the making, according to Byrne, and will transform Weber’s presence in the Nordics, where to date it has operated through affiliates.
Clients the two agencies have in common include Ikea and Electrolux.
Prime was founded in 1998 and its offer spans public affairs, crisis management, digital and social media, corporate communications, and business intelligence.
It is headquartered in Stockholm, employs 130 staff and has a business intelligence arm called United Minds.
Prime founder Carl Fredrik Sammeli and executive creative director Tom Beckman will join Weber’s global leadership team.
Sammeli will report to Byrne while Beckman will continue to report to Prime chief executive Markus Gustafsson but will also become chair of the Weber Shandwick Global Creative Collective, reporting to Weber president Gail Heimann.
Byrne said: "It’s significant that Sweden is the most digitally advanced country in Europe, which is why they do such advanced work in PR.
"Our strategy is to deliver the best thinking in the world to clients, wherever that comes from," he added. "We want to embrace the new thinking and bring it to a wider audience."
This article was updated on 7 May with quotes from Colin Byrne.