A nonprofit organisation that claimed it could turn gay men straight violated New Jersey's Consumer Fraud Act, a jury concluded in a civil trial that an attorney for the plaintiffs called "a momentous event" for LGBT rights.
The jury said that Jews Offering New Alternatives for Healing, co-founder Arthur Goldberg and counsellor Alan Downing made misrepresentations and engaged in unconscionable business practices.
Three men and two parents were awarded more than $100,000 in damages.
The judge will rule later on their request to revoke the company's license, plaintiffs' attorneys said.
"This is a momentous event in the history of LGBT rights," attorney David Dinielli said. "The same lies that motivate gay conversion therapy motivate homophobia - that gay people are broken and need to be fixed. The strength of our plaintiffs brought that to light."
Attorneys for the plaintiffs argued during the trial that the group, known by the acronym JONAH, claimed a success rate that wasn't backed up by actual statistics and used therapy methods that had no scientific basis, including having one client beat a pillow, meant to represent his mother, with a tennis racket.
In an emailed statement, defence attorney Charles LiMandri called the verdict "a sad day, not just for my clients, but for America."
LiMandri said he would "seek justice on appeal."