The deal comes hot on the heels of Tesco taking a 91 per cent stake in the internet radio service We7 in June and its acquisition of movie and TV streaming service blinkbox in 2011.
Mobcast, which was set up by McNab and its chief executive Tony Lynch in 2007, has a catalogue of more than 130,000 books available to download onto smartphones, tablets and e-readers. As well as its own online shop, Mobcast also provides retailers and mobile operators with a platform to sell their own ebooks.
McNab and Lynch own 40 per cent of the company, meaning the two will share around £2m of the proceeds.
McNab said: “As an author I always thought the ability to carry your library around and read on all your personal devices would be a huge benefit to all... being acquired by Tesco ensures that this original vision will be available to as many people as possible.”