Following the pilot in Cambridge, ofo will roll out the service in the summer to a number of other UK cities including London, a spokeswoman for the agency said.
The app-based service has already launched fully to the Singapore and Chinese markets, and been trialled in San Francisco.
Manifest founder Alex Myers said ofo was "already a disruptive business that is making its mark globally - so it's exciting to help steer the brand's evolution and success in the UK".
Manifest's brief includes PR, brand consultancy and content creation, and the agency will also handle ofo's UK social media strategy and influencer marketing activity. The agency will host a media briefing for Cambridge's local press in April.
Peking University graduate Dai Wei founded ofo in 2015, and last year received $450m (£359m) funding from investors, including Didi Chuxing, to grow the business.
The service allows customers to find, unlock and rent its yellow bicycles via the company's smartphone app. Unlike London's existing 'Boris Bike' scheme, officially called Santander Cycles, ofo operates a non-docking system and monitors the location of its users' smartphones to "redistribute and repair" bikes, the company said in a statement.
The Manifest spokeswoman added: "Boris Bikes are a great example of how to mobilise a city, however, the restrictions with docking stations means it doesn’t offer the best flexibility for users. The London launch will be focused on offering Londoners a new way to explore their city and to get more people on two wheels."
The win comes a week after Manifest announced it had promoted director Neil Hallmark to MD of its London office.
• Click here to subscribe to PRWeek – you'll get essential breaking news, views & expert analysis; an exclusive UK Daily News email bulletin; industry-leading reports such as the Power Book, Global Agency Business Report, Best Campaigns & Best Places to Work; and a whole lot more.