In 2000 she played her first tournament on the ITF Women's Circuit in Hull . In 2005 she was able to win the tournament. The following year she won the ITF tournament in Nottingham and in 2009 the tournaments in Sutton and Jersey. In 2003, O'Brien was British Junior Champion in singles and doubles.
Her best performance in a Grand Slam tournament was reaching the second round in 2007 at Wimbledon and in 2010 at the Australian Open . In doubles, she did not get past the first round at Wimbledon. She took part in competitions at Wimbledon 16 times, but only four times in other Grand Slam tournaments.
She played her last professional tournament in Wimbledon in June 2011 when she lost to Kimiko Date Krumm in the first round of the main draw with 0: 6 and 5: 7. Since June 2012 it has not been included in the world rankings.
Katie O'Brien is studying business administration at the Open University . She has a brother and a sister.