The Cally Palace and golf course have been put up for sale along with the other two McMillan Hotels in the group.
The McMillan family took the decision to sell after the next generation all chose careers outwith the hospitality trade.
Around 150 people are employed across the three hotels which have been very busy since reopening after lockdown.
Purchasing manager Fay Cowan told the News the family’s main priority was finding an appropriate buyer.
She said: “We could be here for a long time yet.
“I imagine it could take a couple of years to find the right buyer.
“We expect everything to go on as normal and hopefully the buyer we find will have deeper pockets than us and invest a lot of money in the business.
“Lockdown was a devastating time for all hospitality businesses, not just us.
“But trading has been great since we reopened and all hotels have been pretty much full since May.”
The company was founded by Hammy and Janet McMillan in 1960 and McMillan Hotels acquired The Cally in 1980.
Fernhill in Portpatrick and the North West Castle in Stranraer comprise the other hotels in the group.
Hammy and Janet are now retired and son Douglas is the managing director.
Daughters Fay and Gail work in the business along with son-in-law Graham Cowan and daughter-in-law Susy McMillan.
Fay said: “Most of the 13 grandchildren have also worked in the business at one time or another.
But over the years, as things have changed within the family it has became clear the next generation have all chosen to follow different career paths.
“The family has therefore reached the decision that new owners should be sought to take the company on into the future.
Fay Cowan went on: “Staff have been informed that this process has begun and Graham & Sibbald have been chosen as agents for the sale.
“The aim is to pass on a much-loved family business, in the best possible condition and in the best possible way to its future custodians.
“The future owners will be experienced hoteliers with ambitious plans for the future of the company and secure funding.
“The family will take as long as is necessary to find the safest hands for their business.
In the meantime, it will be business as usual. All 150 jobs are secure.
“When the time comes, staff will automatically be transferred over to the new employer under TUPE regulations.”
She added: “We know that the area is on the increase for tourism – you can see that in the bookings.
“The South West 300 Coastal Route will bring a lot of people in – it’s a super driving route. I have to replenish our shelves every day with 20 more maps.
“The McMillan Family will continue to work hard for the future of the company and we hope that our staff and our loyal customers will continue to support the hotels in their usual way.”