Jenner, 65, revealed he is a transgender woman in a two-hour exclusive interview with Diane Swayer.
Transgender actress Laverne Cox congratulated Jenner on his decision to come forward, tweeting at the reality star.
"Sending lots of love and support to #BruceJenner and their family tonight. It is always brave to stand in one's truth. Congrats darling."
"#BruceJennerABC Now that is bravery. We have the chance to write this moment in history together. Let's empower people like Bruce all over the world by being loving & not mean," tweeted Gaga.
"LOOOOVE LOOOVE LOOOVE Bruce Jenner," tweeted Cyrus.
TV host Jimmy Fallon, while praising Jenner, wrote, "One small step for man, one giant leap for mankind. #BruceJenner #Brave."
"Guess what I got news for you: the Kardashians are not the problem with America Dear Stranger: if you're making unkind Bruce Jenner jokes you have me to answer to. I seriously feel protective this week," tweeted Dunham.
