Cornwell, who was responsible for Spain, traditional France, South America and sparkling and Champagne, had been at the retailer for seven years. She has more than 10 years' experience in the wine trade, including roles at Majestic and Moreno Wines.
Cornwell said: "Morrisons provided an invaluable training ground and, although I am sad to leave a great company, I look forward to the challenges going producer-side will involve and to grow an outstanding portfolio of wines."
She will be looking after key retailers and focusing on both sherry and wine at Gonzalez Byass.
UK managing director Martin Skelton said: "Suzie brings a breadth of experience and insight from her time as wine buyer which makes her a valuable addition to the company. She joins a growing team on the wine side of the business, indicative of our determination to make a mark on the UK market in 2009."
Cornwell's move comes after a number of departures from Morrisons' BWS team last year. Licensed trades director John Spurs retired; wine trading manager Stuart Purdie left after 16 years at the supermarket "to pursue other interests"; James Jackson, who had been responsible for Italy, Vin de Pays d'Oc, California and low alcohol wines, moved to the group's food department; and senior spirits buyer Jane Pearson also left.