Three Thai man have been arrested, police said.
The trio - a security guard and chef at the resort and their friend - were arrested and confessed to killing the couple and taking a mobile phone and 5,000 baht (£103).
The bodies of Michael Raymond, 68, and Suchada Bowkamdee, 52, were discovered on Tuesday in their bungalow at the Jack Beach Resort in Prachuap Khiri Khan province, 220 miles south of Bangkok.
He says they had checked in a day earlier.
Police said two of the three suspects were addicted to methamphetamine and needed money to buy drugs.