Scott Howard stopped working with Kudrow in 2007 and sued her in 2008 for not living up to an oral agreement he said they made, in which he would receive a portion of her earnings from the show.
Although Kudrow denied they had such an pact, TMZ reported the jury found in favor of the plaintiff Wednesday.
Kudrow's lawyer told the celebrity news website the "Web Therapy" and "Scandal" actress plans to appeal the verdict.
"Friends" was a top-rated sitcom during its 10 seasons on NBC, which wrapped in 2004. It remains popular in reruns.