Talking to Media Week as part of an extensive investigation into the impact of the credit crunch on media, the man who counts MediaCom, Mindshare and Mediaedge:cia among his £7.5bn communications empire, draws upon the group's 23 years in business to support his stance.
"Our view is that when times are tough, it's the time to invest not cut," said the chief executive, currently embroiled in an aggressive takeover bid of research specialist Taylor Nelson Sofres. "This comes from years of research dating back to Ogilvy's Alex Biel in the eighties and Millward Brown's interaction surveys before then.
"Industry research has consistently shown that if we cut marketing during such times, the impact is damaging and it can take you longer to get back to where you were."
At the helm of the far-reaching WPP, active in more than 100 countries, Sorrell admits to an enviable position of near double-digit growth throughout Asia-Pacific, Latin America, Africa, Middle East and parts of Central & Eastern Europe.
However, he does expect a global correction of sorts, refusing to believe the world can be so "decoupled". Fuelled by GroupM insights, Sorrell has been flagging 2009 as a difficult year, but urged companies to resist the temptation to slash marketing budgets.
"Of course, it's easy to say, but harder to do," he admits. "The Pavlovian reaction is to cut, but I think the media industry can learn from someone like Rupert Murdoch, who historically has never done that.
"You'll see him investing in editorial and products at a time when other people are throwing the baby out with the bath water."
Sorrell also remains optimistic that the current downturn does not need to be a prolonged affair, predicting the financial markets are likely to pick up by mid-2009, "almost as quickly as they fell away".
If this is the case, a "real world" recovery can be expected in the "mini-quadrennial year of 2010", he adds, when recovery will be aided by five key global events: Mid-term US elections, Winter Olympics in Vancouver, World Cup in South Africa, Shanghai World Expo and the 16th Asian Games in Guangzhou, China.