The new deal will freeze energy prices until 31 March 2018, which is three months longer than the previous longest fix offered by Npower.
Sainsbury’s Energy’s tariff will cost the average consumer £1,316 a year, although it does come with a £50 per fuel cancellation fee.
British Gas is the partner for Sainsbury’s Energy and provides the electricity and gas for the white label supplier.
Tom Lyon, energy expert at Uswitch.com, said: “While many consumers have been left disappointed by the way suppliers have handled the levy-led price cuts, the launch of a new longest fix term plan on the market shows that competition is still alive and kicking.
“This new offering from Sainsbury’s Energy gives consumers over four years of sanctuary from future price hikes.
“This peace of mind makes it a strong contender in today’s market albeit that it comes with a hefty price tag.”