The promise will ensure that the supplier’s variable tariffs will not see any increase in standing charge or unit rates until after the coming winter.
The guarantee comes after it has emerged that the six major suppliers are expected to increase their prices in the coming weeks.
Ian McCaig, chief executive of First Utility, said: “The rising cost of energy affects us all and many consumers will be worried about how it will impact their bills this winter.”
He added: “Our promise will protect families from feeling the brunt of energy cost increases during the coldest months.
“As the largest UK independent, we believe we have a responsibility to loosen the hold the Big Six has on the UK energy market for the benefit of the hard pressed consumers and our winter price hold supports this ambition.
“We encourage the big six to follow our lead and guarantee peace of mind for worried customers this winter.”
Ann Robinson, director of consumer policy at Uswitch.com, added: “First Utility is a small supplier, but making some big waves in the market.
“While the big six appear to be squaring up for price hikes, this relative newcomer is throwing down a gauntlet by declaring a price freeze.”