British Airways and Bangkok Airways will begin codesharing from 11 June.
The Oneworld alliance member will place its code on Bangkok Airways-operated services from Bangkok to Koh Samui, Chiang Mai and Phuket, and from Singapore to Koh Samui, says BA.
"This new partnership will offer smooth transit for passengers travelling from long-haul routes with BA to Bangkok and Singapore for their onward journey to Thailand's key destinations namely Koh Samui, Phuket and Chiang Mai," says Bangkok Airways' senior vice-president for network management Peter Wiesner. "We believe this partnership will offer a unique advantage for BA customers who will enjoy our unparalleled services which include free lounge access, in-flight meals and more. I am confident that this will also strengthen Bangkok Airways' extensive codeshare scheme as well as boosting tourism in Thailand and Asia."