ITV will pay Sky Ventures £10 million for its 49.5 per cent stake in GSB, which runs the Granada Plus and Men and Motors channels.
The move enabled ITV3, which focuses on "vintage" programming, to launch on Sky's digital platform on Monday, replacing Granada Plus on channel 119. ITV3 was due to launch solely on digital cable and Freeview.
ITV's sales department will enter into negotiations with media agencies over the transferral of any existing deals with Granada Plus.
Sky has also bumped ITV2 to channel 118, up from 175.
Granada Plus, which airs old shows such as The Sweeney, will now be wound down. Some of its more modern content, such as Cracker and The Darling Buds of May, will pass over to ITV3.
ITV's chief executive, Charles Allen, said: "We are delighted ITV3 is available on all digital platforms from launch, reaching the widest possible multi-channel audience. This deal delivers on our objective to build the ITV family of digital channels and will enable ITV3 to maximise its potential."