The "Boyfriend" hitmaker was vacationing in Bora Bora in French Polynesia when he came across bride Katie Wollesen and her new husband and sang for them as they sat down to eat, reported Femalefirst.
But the evening then took a more raucous turn as he joined them in a drinking game.
Posting a picture on Twitter of herself and a female friend, Katie wrote: "Thank you @justinbieber for serenading us at dinner, challenging us in flip cup, and leading the winning team in the first annual coco bowl! #honeymooninwiththebiebs.(sic)"
The 21-year-old singer also shared a photo of himself with the newlyweds and other friends on his Instagram, in which he was carried topless by the group.
He wrote: "Met and hung out with the coolest married couples last night and then this happened (sic).