Summer protests by Northern Irish farmers have struck a chord with the multiples.
Beef producers joined their Scottish and Irish counterparts in picketing supermarkets last month in protest against South American imports.
Sainsbury has now said it will source 100% local beef from October, only bringing in beef from Britain when seasonal demand exceeds supply.
The chain, which now has a dedicated Northern Ireland unit, also said summer promotions had boosted sales of Northern Irish beef seven times over.
Tesco has confirmed the end of its short-term special offer on Brazilian beef across the UK.