Travellers will be able to get up to 60 minutes free access per day when they register to use the service.
A London Overground spokesman said Wi-Fi would be available at 12 key stations. He said these would be high-traffic stations, such as Willesden Junction and stations near the Olympic park in east London, including Hackney Central, Hackney Wick and Dalston Junction. It will roll out to all 56 London Overground-managed stations by the end of the year.
The news comes shortly after Virgin Media announced it had been selected by Transport for London to power Wi-Fi and mobile internet services for the London Underground, in time for the Olympics.