M&S is to close its energy business in a move that will impact around 60,000 customers.
Anyone who is affected will be moved over to Octopus Energy in the next few weeks.
Octopus Energy already supplies the gas and electricity to M&S Energy customers on behalf of the firm.
But the move means Octopus Energy will soon manage all M&S Energy customers directly.
The switch will take place automatically and customers will not need to do anything to be moved over to Octopus Energy.
M&S Energy released a statement on its website which reads: "From April 1, 2023, M&S Energy will become Octopus Energy.
"All our customers will continue to receive honest pricing, 100% renewable energy and outstanding customer service, however we're not accepting new customers at this time."
Have you had trouble with your energy supplier? Let us know: mirror.money.saving@mirror.co.uk
If you have a question about your M&S Energy account, you can email hello@mandsenergy.com.
Alternatively, you can call 08081 697 822 if you'd rather speak to someone over the phone.
Octopus was recently came top in the Which? annual customer energy survey with a combined score of 78% based on customer feedback and an assessment by the consumer champion.
The energy provider was also the only company to get a five-star rating in any category and nine in ten customers said they would recommend it as a supplier.
Kirsty Ward, M&S Connect director said: "We want to simplify our services offering and focus on serving our customers brilliantly and giving them more reasons to shop with us.
"As a result, we have decided to step back from providing energy and ultimately, our partnership with Octopus Energy.
“All existing M&S Energy customers have already been contacted and there is no action required from them."
An Octopus Energy spokesperson said: “Over the last five years M&S Energy, powered by Octopus Energy, grew to serve around 60,000 customers, all while maintaining five-star customer service ratings on Trustpilot.
“As a result of M&S exiting their energy supply business to simplify their services, all M&S Energy customers are now switching over to Octopus, where they will enjoy the same rates and world-class customer service as before.
“Customers don’t need to worry or take any action.
“There will be a smooth transition and no disruption to their supply and customers have already been contacted about the next steps.”
