During this time he courted the attention of foreign clubs, such as Brighton & Hove Albion and the Swedish champions Djurgårdens IF.

[2] Byrne was a key player for Shels in the title winning 2006 season, topping the scoring charts again with 15 goals in 26 league appearances, including a crucial last-minute winner against Derry City.

Following the break-up of the Shelbourne team due to tax irregularities, which saw the club demoted to the League of Ireland First Division, Byrne signed for Cardiff City[4] for a fee of £75,000 on 17 January 2007, and scored on his debut against Wolverhampton Wanderers, after coming on as a 62nd-minute substitute.

[5] He made several appearances for Cardiff, alongside Michael Chopra, toward the end of the season as their promotion push stalled and they found themselves struggling to maintain form.

During the summer it was widely reported that Cardiff had cancelled his contract, even being confirmed by Sky Sports that he had left the club, however this was soon revealed to be false.

[7][8] Byrne wrote himself into Bohemian folklore by scoring the goals that clinched the 2008 title against Drogheda United on 10 October.

On his first start of the 2009 season, Byrne netted a brace as Bohs beat arch-rivals Shamrock Rovers 2–0 on 20 March.

Despite a good run towards the end of the season where he scored an important winner against big rivals Shamrock Rovers,[11] Byrne and Bohs just came up short losing the league title on goal difference.

On 4 December 2010, Byrne signed for Dundalk along with fellow Bohemians teammate Mark Quigley on a one-year deal.

On the final day of the season, coming on as a substitute, he scored a consolation goal in the 90th minute against Shelbourne to make it 3–1.

Ireland lost 1–0 at home, with Byrne a late substitute and setting up chances for Damien Duff and cousin Robbie Keane.