SSE is now part of Ovo, creating the second-biggest energy firm after British Gas, supplying five million customers.
Ovo said that together the firms 'can bring millions more people with us on our journey towards zero carbon living' when it announced the completion of the sale this morning.
SSE's brand will continue to exist for the moment while business leaders plan how to join the companies together.
Keep reading to find out what this means for SSE customers, and Ovo's plans for the future.
Your payments and tariffs won't change and SSE products are still on sale. You can still log in to your online account as usual. If you pay as you go for electricity and gas, your SSE top-up card or key will still work as they did before.
The only difference is that Ovo, instead of SSE, will be mentioned in the small print on your bills.
If there are changes in future, you will be told.
'Absolutely nothing changes for Ovo customers,' Ovo confirmed.
Founded in 2009, Ovo's mission was to provide 'cheaper, greener and simpler energy'. It grew to be the largest independent supplier.
It has committed to achieving net-zero emissions in its operations and supply chain by 2030. Ovo also launched the first domestic vehicle-to-grid charger for electric vehicles.
In our most recent energy companies satisfaction survey, Ovo finished a respectable sixth out of 30 companies included. Customers were particularly enthusiastic about its online customer service, which was rated excellent.
Ovo says that it plans to combine its 'innovative technology and Plan Zero commitments' with SSE's 'history of excellence at scale'.
In future, customers will get more ways to save energy, cut their carbon footprint and keep their bills down, according to the brand.
Now that the purchase is complete, Steven Fitzpatrick, CEO and founder of Ovo, said: 'We have an integration plan that leaders from both companies have collaborated on since September. There is a lot of work to do to bring the two businesses together, but we have a really strong combination of great talent, technology and customer centricity that will enable us to succeed.