Partington thanked the holding company for its willingness to support the deal.
"I'm no stranger to running my own agency and this fulfils my desire to return to doing that. I'm looking forward to building a company that reflects the New Zealand-centric offer we've been developing in recent times," he said.
Partington is one of the most well-known advertising executives in the local ad scene, having helped build Ogilvy into one of the biggest agencies in the country.
Before working under the Ogilvy banner, Partington ran an agency called AdWorks. It was in 2004 when Ogilvy (trading as Singleton Ogilvy & Mather) struck a deal with AdWorks, which saw Partington hand over 65 per cent of his holding in the agency. Given the success of the agency, the international holding company later increased its stake in the business.
With Partington at the helm, Ogilvy made a number of major acquisitions in the mid-2000s, including the purchase of Metromedia and creative agency Meares Taine Creative.
These acquisitions combined with a steady stream of big account wins saw Ogilvy NZ evolve into a formidable brand - particularly in the retail space.
Partington now hopes to continue building on this legacy under the Stanley St brand.
"Our aim is to celebrate the creative and media partnership that has long been central to our client proposition," he said.
The local ownership structure will see Stanley St, which has offices in both Auckland and Wellington, become arguably the biggest independently owned agency in the country.
The company will be led by Ian Rodney, who has been brought in as the newly appointed managing director.
WPP AUNZ New Zealand managing director Sven Baker stressed that Ogilvy would continue to operate in the local market.
"Ogilvy International will invest in creativity and technology, and leverage WPP's global scale and investments, to deliver a fully integrated offer to its clients in New Zealand," Baker said.
Ogilvy International will be led by WPP AUNZ business director Mark Jenner, who will report into Ogilvy Australia chief executive David Fox.