The Canadian pop star rang in his 20th year with a low-key party in Atlanta, having left Los Angeles for the southern city late last month.
Bieber's father, Jeremy, visited Atlanta for the occasion, and tweeted, "Happy Birthday son. Wow 20!"
Jeremy's other children, 5-year-old Jazmyn and 4-year-old Jaxon, also attended the festivities.
"Happy Birthday YOU KNOW WHO! I love you. Xoxo," tweeted Bieber's mother, Pattie Mallette.
"20!? I haven't accepted it yet. Still in denial! I can't believe it! Not a teenager anymore.. Unbelievable. #DoesThatMeanImOldNow?" she added.
love you my little bro.. happy birthday pic.twitter.com/ms5V39dSLL— Johnny Shahidi (@john) March 1, 2014