A British man and his Haitian partner were attacked by dozens of locals who threw molotov cocktails and rocks at the couple's private engagement ceremony, police said.
Several people were injured, two cars were set ablaze and windows were smashed at the residence where the ceremony took place in Port-au-Prince late Saturday.
Police arrived just in time to prevent people being killed, inspector Patrick Rosarion told AFP.
The attack on the British man, identified only as a member of the Red Cross named Max, and his Haitian partner, was a clear example of homophobia, a rights advocate said.
"This is a criminal act and homophobic," said Charlot Jeudy, an official from Kouraj (Courage), a group that defends the rights of homosexuals in Haiti.
"There is no justification for this kind of attack on people in a private residence. Hopefully the justice authorities will react to the perpetrators of this act."
The British victim said he was fine but did not wish to discuss the matter for fear of identifying his partner and making him more vulnerable to acts of homophobic violence.
Protestant church members in Haiti have conducted street protests in Port-au-Prince, chanting "no to gay marriage in Haiti." Gay rights organizations have expressed shock at the treatment they have received.