In a statement, Teneo Holdings said that both companies had "been fully incorporated with Teneo's existing UK business", along with Blue Rubicon, which it also acquired in 2015.
London-based Blue Rubicon will retain its separate identity, however.
The company said: "The combined business offers a comprehensive, truly differentiated set of services that encompass all areas of corporate reputational management, including strategic communications, investor relations, financial and digital analytics, corporate governance, government affairs and geo-political risk advisory. Teneo is able to seamlessly integrate these disciplines to create bespoke solutions for each unique client need."
The acquisition of Blue Rubicon and StockWell in July doubled Teneo’s global headcount to more than 500 employees, and created one of the largest strategic comms practices in Europe. The Pendomer acquisition in October added a further seven people.
Speaking to PRWeek in July, Teneo International CEO Charles Watson, who will oversee Blue Rubicon and StockWell in the UK, said: "It’s our intention to grow a global business and what we saw [with the acquisitions] was the first big opening move in what we are currently about."
As PRWeek has reported in recent weeks, Teneo was understood to have been in discussions with APCO about investing in that business, although talks later ended.
Teneo was founded in 2011 by Declan Kelly, the former US economic envoy to Northern Ireland, and Douglas Band, the top comms adviser for former US President Bill Clinton, as well as Paul Keary, a former senior MD of FTI Consulting.