However, the commitment will apply to just four out of the 25 train companies operating in England and Wales.
The DfT will then allocate funding to the four operators for any proposals it deems ‘satisfactory’, so they can start to install the necessary equipment.
The remaining 21 train operators are ‘being asked to set how they will meet the commitment’, the department said.
It added: ‘Some operators have already installed equipment to provide improved mobile coverage on-board their trains, or are in the process of doing so.’
The money comes from a £53.1 million fine Network Rail paid for missing the regulator’s punctuality targets last July.
Of that total, £5.3 million has been allocated to the devolved Scottish government, with the remaining £47.8 million available to England and Wales, a DfT spokesman explained.
All train operators bidding for new franchises and agreements from 2017 will have to include a commitment to provide free wi-fi in their bid, the government promised.
French state railway firm SNCF has promised to connect the entire train network in France to the internet by the end of 2016.
It will achieve the target by increasing wi-fi coverage, but also by improving mobile 3G and 4G networks.
Chief secretary to the Treasury Danny Alexander said: “As someone who regularly travels from the north of Scotland around the country, I appreciate the value of fast, cheap internet connections on trains for both leisure and business travellers.
“That’s why the government is earmarking around £50 million to provide free wi-fi on trains; this and our other franchising improvements mean that nearly three-quarters of rail journeys will be made on trains with wi-fi provision.”
Image credit: ©iStock/monkeybusinessimages