George, most recently the chairman of MEC in UK and Northern Europe, takes over at a crucial moment for Group M, which has merged his old agency with Maxus to form Wavemaker and is seeking to build up sister digital agency Essence into a full-service media network.
Theakstone, a tough negotiator who built Group M into a formidable operator in the UK, will oversee more than $100 billion in annual billings for the world’s biggest media buyer.
Theakstone is the fourth UK chief executive at one of the big six media-buying groups to leave their role since October after changes at Publicis Media, Dentsu Aegis Network and Havas but, unlike some of those rivals, Group M has been performing well.
"Group M has done more than OK in the UK – in our opinion," Kelly Clark, the global chief executive of Group M, said, noting Britain is the group’s biggest market after north America. "In some ways, that has led to Nick Theakstone’s promotion."
Clark said George’s task was "to continue to grow Group M, to continue to grab market share, to increase client engagement and to innovate and create new products" in the UK.
Both George and Theakstone are moving to new roles at a time when media agencies face multiple challenges, including advertisers buying directly from Google and Facebook, consulting giants such as Accenture muscling into the ad market, and fears about online brand safety and agency transparency.
Theakstone has international experience despite running the UK for the last decade as he has sat on Group M’s European leadership team, working alongside both CEOs and heads of trading from other countries.
Group M has previously had a global chief investment officer but the role has been unfilled for several years and the market has changed radically because of the rise of the tech giants, which means media budgets are increasingly being managed globally, not just locally, according to Clark.
He said Theakstone’s role was important because "trading is the most important thing that Group M does" and it offers a "tangible" benefit to clients when there has been "this consolidation of trading power with Google and Facebook and, increasingly, with Amazon and others".
In his new role, Theakstone will "develop strategies to ensure the benefits of Group M’s scale continue to deliver advantages to clients as trading becomes more data-driven and technology-enabled", the company said.
Theakstone will be based in London and New York, where he is expected to spend "a significant amount of time".
Johan Boserup, Group M’s global head of trading, will report to Theakstone.
The appointments of George and Theakstone came at the same time that WPP promoted Karen Blackett, the chairwoman of MediaCom UK, to be its first UK country manager.
The job changes at Group M UK have been expected since the summer.
Multiple sources claim there was a delay because Group M came under internal pressure to ensure the appointment of Theakstone’s successor was not a fait accompli and that there was a "thorough" process.
Clark dismissed those suggestions as "idle gossip". He said "we like to plan things carefully" and the job changes had taken time "mainly out of concern for our clients and our teams".
Under Theakstone’s leadership, Group M UK claims to have quadrupled in size in a decade, taken market share each year, and is double the size of each of its three nearest competitors, Publicis Media, Omnicom Media Group and Dentsu Aegis Network.
"By every measure, our people, our agencies and businesses are market leaders and I can look back with pride on all that has been achieved," Theakstone said. "It’s also been fun."
He was an innovator who pushed programme finance, which meant Group M received advertising air-time in return for funding TV shows.
He also showed toughness when he pulled all Group M’s media spend from Channel 4 at the start of 2013 in a trading dispute and he claimed it was an "insult" for ISBA, the trade body for UK advertisers, to suggest media agencies no longer have clients’ best interests at heart in a row over agency transparency in 2016.
George spent the early part of his career at Bates Dorland and Zenith. He joined MEC in 2005, becoming UK managing director and then UK chief executive, before taking on the role of chairman for UK and Northern Europe in 2011. He was also global head of business development.
As UK CEO of Group M, he will report to Dominic Grainger, chief executive of Group M EMEA.
George said he was keen to improve the reputation of the media agency sector.
"As the dominant player in the UK, I think we need to take more of a leadership role," he said.