He began working part-time at Musgrave's C&C in Belfast while he was a student, "a great grounding in the business".
When he graduated with a degree in building and management, he found there were no jobs in his chosen field as it was in the middle of a slump, so he accepted an offer from Musgrave to manage the non-food department.
"The experience was invaluable. Now I'm never asking people to do something I haven't done."
Including Donnelly and two assistant managers, there are 25 staff at the depot. One of the strengths of the business, he says, is its closeness to the community.
At 22,500 sq ft, the depot is smaller than many of its counterparts on the mainland. The staff know many of their customers and their businesses well, and understand their needs.
Most retail customers run CTNs, he says, and time spent out of their shops at the cash and carry is costing them money because they have to pay staff to run the store while they are away.
This means they want to be in and out of the depot as quickly as possible, so Donnelly and his team have worked to merchandise the depot to enable customers to find what they are looking for as quickly as possible. An alternative is Holmes' thriving delivered business, which can offer same-day delivery.
Donnelly emphasises that he sees his role as not just staff management, but wider business management where he can make a difference to the financial performance of the depot.
Using his knowledge of his customers, he is able to negotiate with suppliers to run weekly and even daily promotions within the depot to complement Holmes' promotional programme.