Tony Keating, CEO of the retailer's franchise partner SSP UK, confirmed he was in discussions with health trusts across the UK and expected to complete deals on two sites this month.
Sales at the first M&S hospital franchise, which opened in March at St George's Hospital, Tooting, had exceeded expectations, he claimed.
"As a result, we are now looking at the hospital market closely because it is an area we expect to grow strongly in," he said. "I think the stores will be successful because they will appeal to busy staff who work shifts and want good-quality food at reasonable prices. Also, patients and visitors can buy food to take back to the wards."
Keating was confident the model would prove successful. Hospital shoppers tended to have more time on their hands and were likely to pay more repeat visits than commuters, he said.
"We have 33 rail station stores and are at a stage where we are approaching the end of our roll-out," he added. "In terms of the hospital market, we have the scope to really grow."
However, he admitted that the hospital market was not likely to be as lucrative as the M&S rail station and airport franchises. The Tooting store currently attracts three million potential customers a year a fraction of the 125 million who could shop at M&S's Waterloo station store.
Keating also revealed growth plans for SSP's Whistlestop food market brand and said he hoped to open new franchises alongside the proposed M&S stores. "Whistlestop trades alongside M&S at the hospital in Tooting and we have found they complement each other because their offerings are different.
"A hospital is going to want a shop that offers newspapers, magazines and confectionery, like Whistlestop does, so we will be proposing new stores to open alongside M&S. But it all depends on the sites available."