The actress was among the 17 million people who tuned into the Olympian's interview with Diane Sawyer.
"It's fantastic, very brave. I wish him well on his journey. I think it's great that he's sharing it with us," Fonda told E! News at the premiere of her new Netflix series "Grace and Frankie".
Her co-star Lily Tomlin said, "I think it was good and brave."
The series revolves around two women who share a love-hate relationship but they grow close once their husbands (Martin Sheen and Sam Waterston) announced that they're in love with each other and plan to get married.