Equitix will pay £40 million (€54 million) for the stake in the licence. The OFTO licence holder is responsible for the operation and maintenance of the link between a wind project and the national grid.
UK energy regulator Ofgem awarded Balfour Beatty the 20-year Thanet licence in December. Thanet, developed by Vattenfall, was part of the first round of tenders for OFTO licences in 2010.
Balfour Beatty was named as the preferred bidder for the licence then, but technical issues with the transmission have delayed the transfer.
Balfour Beatty and Equitix have also partnered, as part of a consortium, on the OFTO licence for the 504MW Greater Gabbard project. And last week, the companies were awarded the licence for the 576MW Gwynt y Mor project in the Irish Sea.
The companies also qualified to bid for licences for the 219MW Humber Gateway and 210MW Westermost Rough projects currently being developed off the north-east coast of England.