E.ON Next will take on customers of the three suppliers that went under last week, ENSTROGA, Igloo Energy and Symbio Energy.
The company will keep supplying the combined total of almost 233,000 customers who have been affected by the closures.
The regulator said that energy supplies for these customers will continue as normal after the switch to E.ON Next on 3rd October.
The customers are expected to be contacted in the coming days about the changes.
Neil Lawrence, Ofgem’s Director of Retail, said: “We understand that this news may be unsettling for customers, however, they do not need to worry. Their energy supply will continue as normal and customer credit balances will be honoured.
“Your energy supply will not be interrupted. E.ON Next 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.”