The retailer has struck a deal with Scottish and Southern Energy that will allow shoppers to enter into energy contracts with M&S at 62 stores across the country from the end of next month or via its website from Monday October 27.
SSE said M&S Energy customers will pay the same price as its existing customers who take gas and electricity and pay by direct debit. The average user pays £1,196 a year.
A key feature of the offer will be customers receiving store vouchers as incentives to encourage them to reduce energy useage.
Those cutting their annual use by 10% in the first year will receive a £15 M&S voucher and those opting for paperless billing will receive an additional £10 voucher.
Duel Fuel customers switching to M&S Energy will also receive a £20 M&S voucher on signing up and a further £10 voucher for each year they remain with the company.
M&S is hoping the offer will also take the confusion out of buying gas and electricity in addition to scoring points with customers who are environmentally friendly.
The new energy offer is part of a push by M&S into new areas in a bid to expand its range of services as it comes under pressure from tough trading conditions. The retailer is now selling branded electrical goods and is also trialling branded foods in 19 supermarkets in the north-east.
Separately, M&S recently launched a series of celebrity TV ads as part of its famed food campaign, famously dubbed 'food porn'.
Instead of the breathy tones of long-standing voiceover provider, 'Ballykissangel' actress Dervla Kirwan, the ads feature celebrities such as 'Only Fools and Horses' star David Jason.
The most recent food ad features the voice of former Daily Mirror editor Piers Morgan in a spot promoting the retailer's steak.