Irwin left Spar, where she was trading controller for wine, in February 2012 to become commercial manager at importer ABS Wine Agencies.
She will take up her new role at Waitrose on December 2.
Liam Steevenson MW is also joining Waitrose as buyer for Australia, Burgundy, New Zealand and regional France.
He has worked for Majestic, Bidendum Wine and Armit and has been running his own Devon independent wine merchant Red & White for the past nine years.
Steevenson starts next Monday, November 4.