The accident occurred on Friday at about 2.30pm when a pickup truck ran over Peter Root and Mary Thompson, both 34, while they were riding their bikes in Chachoengsao's Phanom Sarakham district.
The pickup truck driver told police that his vehicle hit the British couple while he was reaching down to pick up something.
The Guernsey couple's bodies are being kept at Phanom Sarakham Hospital.
Reports said the British embassy was contacting their families so they can bring the bodies back home.
The couple had started cycling around the world two years ago, and had travelled to Europe, the Middle East, China and 23 other countries.
The pair, who met 14 years ago as art students, updated their adventure on www.twoonfourwheels.com.
View the original story on the Bangkok Post here.