A left-handed player from Dublin, O'Halloran played college tennis in the United States before turning professional.

[1] From 1986 to 1998 she featured in 32 Fed Cup ties for Ireland, winning 20 matches, 5 in singles and 15 in doubles.

She made it into the women's doubles main draw at the 1989 Wimbledon Championships, as a lucky loser from qualifying, with American partner Leigh-Anne Eldredge.

[3] O'Halloran currently holds the position of Director of Rackets in Fitzwilliam Lawn Tennis Club in Dublin.

She has competed on the ITF senior circuit and finished 2012 as the world's top ranked player in both singles and doubles for the 45's.