Robin Wight, Leon Jaume and Stephen Woodford, WCRS's chairman, executive creative director and chief executive respectively, began talks with Havas last summer to negotiate an exit from the French holding company.
It is believed that the management team, who have been joined by the agency's former managing director Peter Scott, paid in the region of £20m to take control of the agency.
The deal, effective as of April 1, sees the French firm retain 25% of WCRS, which will continue to act as the UK office of the Havas advertising network Arnold Worldwide Partners.
The completion of the buyout comes as the agency, once known as Wight Collins Rutherford Scott, is on a new-business roll picking up the £15m Phones4U through-the-line account and a TV campaign for mobile phone network 3.
Havas said the deal reflected a mutual desire to develop the interests of WCRS and Arnold Worldwide, by allowing the management to buy into the agency and Arnold to retain a significant minority stake.
"Both parties believe that this deal will spur WCRS forward to achieve greater success and mean that Arnold has as strong a partner as possible in the crucial UK market," Havas said.
The management buyout sees Wight become joint chairman of the new company with Scott, while Woodward remains as chief executive.
It is understood that the management team raised the cash themselves, steering well clear of venture capital backing.
Last month WCRS launched the latest phase of its highly successful campaign for directory enquiry service 118 118 as its moustachioed runners transformed into jump-suited 1970s crime fighters.
If you have an opinion on this or any other issue raised on Brand Republic, join the debate in the Forum here.