The fast food company said it will no longer be supplied by food processing plant Silvercrest. Instead, it is moving to find a company that can provide 100% pure Irish and British beef products.
It is the latest in a series of contracts lost by the Co Monaghan firm, which is part of the ABP Food Group.
Tesco, Aldi and the Co-operative Group have all taken their business elsewhere, following the revelation last month that a filler product used in the burger processing facility contained a mixture of beef and horse offcuts.
Burger King said Silvercrest had violated their contract by failing to deliver 100% British and Irish beef patties.
Test results at the plant revealed "very small trace levels" of horse DNA in Burger King products, but burgers taken from restaurants tested negative.
The company's Vice President Diego Beamonte said they had failed customers.
"While the Food Safety Authority of Ireland has stated that this is not a food safety issue, we are deeply troubled by the findings of our investigation and apologise to our guests, who trust us to source only the highest quality 100% beef burgers," he said.
Our supplier has failed us and in turn we have failed you. We are committed to ensuring that this does not happen again.
Diego Beamonte, Burger King Vice-President
"We will dedicate ourselves to determining what lessons can be learned and what additional measures, including DNA testing and enhanced traceability controls, can be taken to ensure that we continue to provide you with the quality products you expect from us," he added.
The horsemeat contamination has been investigated by Irish authorities, who said the filler product has been traced to a Polish supplier.
Burger King said its own tests on restaurant burgers came back negative for equine DNA, but Tesco has revealed some of the burgers they had been supplied with were 29% horse.
The Co-operative Group announced independent tests of its own-brand burgers supplied by Silvercrest had found traces of less than 1% horse DNA in three samples and 17.7% in one sample.
On Wednesday experts from the Food Standards Agency told a House of Commons committee they cannot be sure if the contaminated burgers were being sold for more than a year.
At least 10 million burgers were put into storage following the scandal and ABP initially said they would be destroyed.
The contamination scandal is thought to have cost Silvercrest around €45m in lost deals with Burger King and Tesco.