Origin operates an all-Ireland grain and animal feed business in conjunction with Belfast-based W-R Barnett.
The change comes some 10 months after Origin bought UAP and is hoped to simplify Origin’s agronomy business in Britain.
With 25,000 customers, Agrii will be a market leader in agronomy services to farmers there.
Origin chief executive Tom O’Mahony said the decision to merge the two brands was a "key milestone".
“Agrii represents a key milestone in bringing together two of the UK’s leading agri-service
organisations onto a single platform," he said.