The service, dubbed Freesat and announced at ITV's interim results, will complement Freeview, the digital terrestrial service that is currently in more than five million homes.
It is designed to appeal to viewers who do not want to pay a subscription but are unable to receive Freeview.
It will compete with Sky's own Freesat service, which offers 120 TV channels for a one-off installation charge. It had a soft launch last October.
Charles Allen, the ITV chief executive, said: "Freesat and Freeview will enable everyone in the UK to enjoy a range of quality channels for free."
With the launch of the service, ITV will be able to broadcast its channels "in the clear", dispensing the need to pay Sky for encryption.
The service will carry other broadcasters, although Channel 4 will not be among them in the foreseeable future because it has recently renewed carriage deals with Sky.
ITV recorded an increase in pre-tax profits of 60 per cent to £205 million and a 3.4 per cent growth in net ad revenue.