The 10-year deal will see the caterer operate the cafés and restaurants and provide hospitality and conferencing at its campus on the edge of Brighton. The contract was won by Chartwells following nine-years in charge of the café at the university's innovation centre.
More than 13,000 students and 2,000 members of staff will benefit from the new service, which begins 1 September.
McKellar, owner of the Gingerman Restaurant in the seaside city, is known for uncomplicated, full-flavoured food using the high-quality seasonal products, Compass said. He has been brought on board to help produce menus that draw on the Ginger Chef's knowledge of local sourcing.
Robin Mills, managing director of Chartwells, commented: "We have great plans to really enhance the dining experience for students and staff; this starts with the menus and we are really excited to be working with Ben McKellar on these.
"Students today want a range of options that deliver great value for money while also meeting their ethical expectations. Our offer will rival the very best of the high street while supporting local, sustainable and Fairtrade suppliers to provide fresh, tasty food with clear provenance for customers."
Chartwells will invest £1m over five years in campus facilities at the university, including the refurbishment of cafés to enhance the student and staff dining experience. Extended opening hours, and student survival and cookery masterclasses offering nutritional advice and support, will also be made available.
McKellar added: "I am hugely passionate about creating great food using fresh, local produce and this relationship with the University of Sussex and Chartwells is a brilliant opportunity to educate people about all the fantastic produce we have available in Sussex.
"It will also give the university a real taste and flair for Brighton's local food scene, keeping it up-to-date with the highly-creative food movement which we enjoy here in the city."