Liu won her first professional title on March 22, 2015, at an Orlando clay court tournament on the ITF Women's Circuit. At age 14, Liu was the youngest tennis player to win a professional tournament since Anna Kournikova in 1996.
After securing two ITF tournament wins in 2017, Liu was granted a wild card into the qualifying tournament at the 2017 US Open. Liu defeated all three of her opponents in the qualifying tournament, earning her a spot in the singles main draw of a grand slam for the first time. There she was defeated in the first round, in straight sets by Duan Yingying. In their main draw grand slam doubles debut, Liu and Taylor Johnson lost in the first round in Women's Doubles at the US Open.
At the 2018 Wimbledon Championships, Liu advanced to the main draw of the tournament after winning all of her qualifying matches. Liu lost in the second round to the eventual champion Angelique Kerber. Liu was the only player in the tournament to win a set against Kerber.