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 in time for the London 2012 Olympics this summer.
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.
The service will be free to passengers for a limited period over the summer, before being available to Virgin Media broadband and mobile customers, or on a pay-as-you-go-basis.
BSkyB acquired The Cloud in January 2011. It delivers free public Wi-Fi through partners including Café Nero and Pizza Express and also provides Sky broadband customers with access to 10,000 Wi-Fi hotspots across the UK.
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