The deal means around 3.5 million customers will be able to watch ITV1 and ITV Play - the channel's participation channel - live on their mobile phone.
It is the first deal of its kind and gives 3 an exclusive ITV 3G mobile licence for six months. After that, ITV will be looking to extend the service to other mobile networks and include more of its channels.
Details of the service, including the cost have yet to be finalised, but it could be offered free with some contracts. It will launch in autumn.
ITV will be the first UK broadcaster to stream its channels live on mobile.
Bob Fuller, chief executive of 3 said: 'This partnership adds a new dimension to the traditional way our customers watch television.'