Ovo Energy, a Bristol-based company, is to buy a second energy firm's household arm, delivering them an additional 3.5m customers as well as 8,000 new staff.
This follows discussions between energy company SSE and Ovo Energy, where it has been agreed that SSE's household arm will be purchased for £500m.
The deal means Ovo Energy will become the second largest energy supplier in the UK, with only British Gas supplying more customers. The company is already the UK's largest independent energy supplier.
Members of staff to move from SSE to Ovo
Number of customers to move from SSE to Ovo
Ovo Energy was founded in Bristol a decade ago by former city trader, Stephen Fitzpatrick, 41. As Chief Executive, Stephen made headlines lambasting the 'Big Six' energy companies to a Parliamentary select committee.
SSE is selling its household arm following an attempted merger with Npower that was abandoned in December last year.
The government's price caps on energy bills and intense competition have been cited by SSE as a reason for the attempt to move away from its supply arm.
In the year ending March 2019, SSE saw 500,000 customers move away to different energy suppliers. SSE's adjusted operating profits have also fallen. They totalled £297m two years ago but last year they fell to £90m.
The Bristol-based move will see Ovo Energy take over SSE's household arm with £400m paid in cash and the remaining £100m paid in loan notes.