Essence has promoted Tim Irwin, a veteran of former sister agency Maxus, to be chief executive in Europe, the Middle East and Africa.
Irwin replaces Nick Baughan, his former boss at both Essence and Maxus, who has left to become director of agency partnerships at Facebook in the UK.
Christian Juhl, global chief executive of Essence, said Irwin will run the UK and German offices, and focus on expansion in more cities in Germany and in other markets such as the Nordics, the United Arab Emirates and France.
Essence is also looking at Amsterdam as a possible office location if Brexit causes problems.
Irwin has been EMEA chief operating officer at Essence since January 2018 after parent company WPP decided to close Maxus and move its staff to Essence.
Essence, which was founded in 2005 and sold to WPP in 2015, made its name as Google’s media agency with expertise in digital and data-driven marketing. It added traditional media buying skills in areas such as TV when the Maxus team joined.
Juhl said: "Tim’s deep knowledge of our business, our clients’ needs, and the operational and management expertise he has demonstrated since joining Essence, make him the ideal person to lead us through our next phase of growth in the region.
"He led the integration of Essence and Maxus in London, which is our largest office, and he’s built an amazing culture in a short amount of time.
"He’s a good, new-business guy and he’s been involved in a lot of our pitches."
Irwin, who first joined Maxus’ predecessor, BJK&E, in 1999 and stayed after its acquisition by WPP in 2001, said: "Essence has exactly the right mix of talent, business model, service offering and client partnerships necessary to fundamentally move the industry forward.
"I’m thrilled to have the opportunity to work with such an incredible team to help bring these elements together in ways that will change the way people think about what a data science-led agency can do to deliver value to consumers and drive growth for businesses."
Essence now employs about 1,700 people, including 500 in Europe, and has billings of $3.6bn (£2.8bn).
Juhl admitted that adding about 600 people from Maxus and developing the agency’s culture has required a lot of work.
He said: "The challenge remains in front of us to take what we’ve been able to do in digital and do it in analogue channels."
However, Juhl said there was evidence that the Essence/Maxus merger has worked and pointed to three achievements in its first year: winning T-Mobile in the US, integrating former top Maxus clients NBCUniversal and BT, and what he described as "keeping up with Google’s growth and expansion".