John Overend is to step down as chief investment officer at Omnicom Media Group UK, the country’s second-biggest media buyer with control of more than £1.5bn in annual adspend.
Overend, 57, will be an advisor until the end of the year, before departing "to purse fresh challenges within the media industry", OMG said.
Adam Turner, managing director of OMG Investment, will take over Overend’s responsibilities.
Overend is a low-profile figure who wielded clout behind the scenes as Omnicom pushed media owners for better prices on behalf of its agencies – Hearts & Science, Manning Gottlieb OMD, OMD and PHD – and their clients such as John Lewis Partnership, McDonald's, Sainsbury’s Group and Volkswagen Group.
He spent his early career at Dorland Advertising and Zenith Media, before joining PHD in 1998.
Overend has been chief investment officer for 16 years and was a founding partner of OPera, the investment division of OMG.
He played a leading role in OPera’s decision to pull clients off Channel 5 in 2014 in a trading dispute that lasted nearly a year – a move that led to the broadcaster closing its own sales house because it lacked scale and then outsourcing sales to a bigger third party, Sky.
In more recent years, power in trading negotiations has tilted from agencies to the global tech platforms such as Google and Facebook as buying has increasingly focused on data and digital smarts, rather than just scale.
Overend, who is described as "quite old school" by one media owner, has remained an important figure and regularly featured in Campaign's annual list of the top 10 media buyers.
OMG has performed strongly compared with some of its peers in recent years and established itself as a clear number two in the UK media agency market, according to Nielsen figures for the 2020 Campaign School Reports.
Omnicom increased its UK media billings by 22% to an estimated £1.7bn last year, behind WPP’s Group M on £3.3bn, but well ahead of Publicis Groupe on £1.1bn and Dentsu Aegis Network on £851m, although adspend has plunged this year because of the coronavirus slump.
Dan Clays, chief executive of OMG in the UK, said: "We can’t thank John enough for his huge contribution to our business over a long period of time.
"On a personal level, I was a TV buyer at PHD many years ago when John oversaw the TV trading and so it has been a privilege to work with him on the OMG board many years later."
Turner will report to Clays and Johan Boserup, the London-based chief executive of global investment at OMG.
The company said Boserup’s growing involvement "recognises the importance of the UK market for OMG" and Clays said the UK team "look forward to working more closely with Johan".
Overend is one of a number of recent senior departures from OMG, including chief marketing officer Sam Phillips, who left in June.