It follows a competitive process run by the regulator “to get the best deal possible” for customers.
SSE will add 17,000 domestic accounts to its list of customers, including those supplied under a while label agreement with Northumbria Energy.
All outstanding credit balances, including money owed to both existing and former customers of Brilliant Energy, will be honoured.
Customers will be switched over to their new Big Six supplier on Friday, 15th March, following which they can shop around and move to a different supplier, with no exit fees.
Philippa Pickford, Ofgem’s Director for Future Retail Markets said: “I am pleased to announce we have appointed SSE, which will offer Brilliant Energy’s customers a competitive tariff for their energy. Their credit balances will be honoured and their energy supply will continue as normal.
“SSE will be in contact with customers over the coming days with further information. Once the transfer has been completed, customers can shop around for a better deal if they wish to.”