Judge Andrew Rutherford says Peter and Hazelmary Bull broke the law when they turned away Martyn Hall and his partner Steven Preddy in late 2008.
Bull and his wife cited religious objections, but insisted their policy was not solely aimed at homosexuals but all unmarried couples.
Equality campaigners condemned the Bulls' decision.
In a written ruling at Bristol County Court on Tuesday, Rutherford awarded the gay couple 1,800 pounds (about $2,900) each in damages.
"Because we wanted to bring our new dog we checked he would be welcome. It didn't even cross our minds that in 2008 in Britain we needed to ask if we would be," Preddy told reporters Tuesday morning outside the courtroom.
He positively refuted claims that he and his partners' case was, "as some have suggested, a set up sponsored by a pressure group."
Mike Judge, from the Christian Institute, the group which funded the Bulls' defense, told the BBC: "This ruling is further evidence that equality laws are being used as a sword rather than a shield.
"Peter and Hazelmary were sued with the full backing of the government-funded Equality Commission.
"Christians are being sidelined. The judge recognises that his decision has a profound impact on the religious liberty of Peter and Hazelmary."