The Rubis station at the M&S in St Martin's will close at the end of August.
The filling station has been in St Martin's for decades but will close permanently on 31 August this year.
It is to make way for an expansion of the M&S Food Hall, which will nearly double in size.
Before building work begins next year, the pumps and underground fuel tanks need to be taken out and hoardings put up.
The retailer says people employed there will be offered alternative jobs.
The fuel company Rubis says drivers have a choice of their garages in St Martin's and the nearby Forest to fill up.
Greg Yeoman is head of M&S in Guernsey and says that getting planning permission to increase the size of the store from 4,000 to 7,000 square feet means that work can begin:
"It's exciting that the project is getting underway. It is important to note that the store will be open at normal opening hours and it's very much business as usual."
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