A worker at the resort in Thap Sakae district of Prachuap Khiri Khan province, 280 kilometres (180 miles) south of Bangkok, found the badly beaten bodies of Michael Raymond, 68 and Suchada Baokhamdee, 52, Tuesday afternoon in their beach front bungalow.
"They were beaten with a chair and other hard objects," case officer Captain Winai Raila-aied told AFP by telephone.
The couple had checked in at the resort on the Gulf of Thailand a day earlier.
Police have begun questioning possible suspects who live nearby and are waiting for relatives of the couple to check what belongings are missing.
Winai said Raymond had lived in the northeastern Thai province of Khon Kean for two years since he got married.