Byrne started playing as a schoolgirl for Leixlip United before moving to as a goalkeeper to St Patrick's Athletic in the Dublin Women's Soccer League and then agreed to join professional Danish Elitedivisionen club Fortuna Hjørring after completing her schooling.

After spending one year in Denmark, Bryne returned to Ireland because she was homesick and took a job as a secretary with the Health Board.

[2] She also became a European champion with Arsenal in April 2007, when they beat Umeå IK in the 2007 UEFA Women's Cup Final 1–0 on aggregate, a tie in which she made numerous vital saves in the home and away games.

[6][7][8] In 2008 she rejected an offer to join American Women's Professional Soccer franchise Boston Breakers, who failed to match her salary expectations.

[9] Byrne was given a free transfer by Arsenal in December 2016 on the expiry of her contract, after being supplanted in the team by Sari van Veenendaal.

[16] Following the retirement of Ciara Grant, coach Sue Ronan named Byrne the team captain in March 2013.

She previously worked in the Football Association of Ireland (FAI) ticket office[3] and was later employed as a coach in Arsenal's academy.