The two-year Gateway project will involve testing the Meridian shuttle, a milk float-style driverless vehicle, in "various scenarios" around the borough.
The idea is to identify the social, legal and technical barriers to bringing driverless vehicles into an urban environment.
There are 11 partners participating in the trials, including the three brands, who will explore how driverless vehicles could change their business models.
O2 will be bringing connectivity to the Meridian shuttle through machine-to-machine technology. In practice that likely means powering certain "smart" aspects of the vehicle, such as navigation.
The partnership is part of O2's wider exploration of its own future with driverless technology, and follows a similar collaboration with Tesla last year.
In April, O2's parent company Telefonica agreed to power the infotainment system featured on Tesla's Model S, including navigation, web browsing and music.
David Plumb, O2's digital director, told Marketing: "At O2 we believe technology has the power to solve everyday problems – easier, better cheaper and quicker than ever before – whether they be household chores or business processes.
"Our role, as a technology provider to 24 million customers nationwide, is to help people and businesses apply digital solutions to these analogue problems.
"Through our involvement in Gateway, we are part of an innovative project which is doing exactly that, and we are pleased to be part of such a strong multidisciplinary team."
Royal Sun Alliance will be examining the potential impact on the insurance industry. Shell has not responded to a request for comment.
The Meridian shuttle took its maiden voyage this week after transport minister Claire Perry and business secretary Vincie Cable launched the trials.
The Gateway project is one of three driverless car trials taking place in the UK this year, with other tests taking place in Milton Keynes and Coventry, and Bristol.