The victim was walking with another man on Johnston Terrace in Edinburgh when the trio came up and verbally abused them.
One of the three then punched one of the men to the ground and he and a companion then kicked him about the face.
After the attack, the three men ran off and were chased by two passers-by into Castle Terrace, where they lost sight of them.
Police Scotland appealed for information about the assault which happened at around 3.10am today
Constable Neil McIntyre said: "This was a brutal, unprovoked and homophobic attack on an innocent member of the public and I am very keen to speak to anyone who witnessed the incident, particularly the two men who came to the victim's aid before giving chase to the three suspects.
"We have descriptions of two of the men who carried out this vicious assault, and both are described as being white British men in their mid-20s, with one being 5 foot 6 inches in height and the other being 6 foot tall.
"The first man had short, dirty blonde hair, was clean shaven and was wearing a black cardigan or jumper, while his taller companion had olive skin and black hair and was wearing a white top with long sleeves.
"Anyone who witnessed this assault, came to the aid of the victim or gave chase to the suspects, is asked to contact Police Scotland on 101 or they can provide the information anonymously through Crimestoppers on 0800 555 111."
The victim was taken to Royal Infirmary of Edinburgh for treatment after the attack.