Avenatti was doing a panel in West Hollywood that included Mayor John Duran, former federal prosecutor Steve Madison and Mariana Magana Gamero, who is part of the Coalition for Human Immigration Rights of Los Angeles.
During the panel, Avenatti stood up and announced the information to the audience. He said the women claim they were paid "hush money" by AMI Entertainment, Trump and his attorney Michael Cohen. He did not reveal what they were paid to stay quiet about.
"There are three additional female clients of mine that have not been disclosed that were paid hush money prior to the 2016 election, whether it be from Michael Cohen on behalf of the president, an entity that Michael Cohen formed, or AMI," he said.
He added that one of the women claimed to be pregnant at the time, and that he is in the process of getting clearance from his clients to release more details related to the payments. It was unclear if they may have been over affairs with Trump.
"Last time I checked, they weren't just handing out checks to anyone whether they had a relationship or not," Avenatti said.
He also addressed rumors that he may be considering a 2020 presidential run.
"If I do not get a sense that the Democratic Party has the right street fighter and the right person to go up against Donald Trump in the general election, I will absolutely run and I will defeat him - period," he said.
Avenatti gained national attention for representing Stormy Daniels, who filed a lawsuit against Trump. Daniels, whose real name is Stephanie Clifford, said she had sex with Trump in 2006, when he was married, but Trump denies it.
Days before the 2016 election, she was paid $130,000 to stay silent in a deal handled by Cohen. She filed the lawsuit to invalidate the nondisclosure agreement, stating Trump never signed it.
The Associated Press contributed to this report.