Doyle initially played for the club's under 18 side but within weeks had made his League of Ireland Premier Division debut on 25 November 2001 in a 1–1 draw with Monaghan United at Richmond Park.

[5] He then had a successful spell with Cork City, who he joined in March 2003 on a two-year deal,[6] linking up with his former St. Patrick's Athletic manager Pat Dolan, who had recently taken over at Turners Cross.

[7][8] For his form he was awarded the eircom/Soccer Writers’ Association of Ireland Player of the Month for November 2004 [9] Thousands of fans gave him a standing ovation in his final game for Cork City, against Finn Harps, before his transfer to Reading.

[13] Despite having left Cork City, Doyle received a championship medal when they won the League of Ireland Premier Division in November 2005.

Originally, he was signed as a back-up, but injuries to Dave Kitson and then Leroy Lita gave him an opportunity in the first team which he retained thanks to a number of important goals along the way.

He scored 19 in total including the equalising goal at Leicester City on the day the Royals were promoted to the Premier League for the first time in their history, 25 March 2006.

Doyle joined newly promoted Premier League side Wolverhampton Wanderers on 30 June 2009 when he signed a four-year contract for a club record fee, reportedly £6.5 million.

After Mick McCarthy rotated systems using various strikers, he eventually reverted to his previously successful 4–5–1 formation, with Doyle playing the lone front man role.

[28] No bids materialised for the striker though during the Summer 2013 transfer window and he featured instead for Wolves' first team during the first part of the season as one of the few remaining players from their time in the Premier League.

[29] He scored on his debut against Burnley on 1 February 2014, and netted a second goal for the club against Reading, as the team chased an immediate return to the Premier League.

[30] However, a knee injury sustained against Birmingham City saw him spend a period back at Wolves during March and April as he underwent treatment.

After returning to Loftus Road,[31] Doyle featured in all three games of QPR's successful play-off campaign as they won promotion back to the Premier League.

His final appearance during his loan spell saw him score his only goal for the club when he netted in an FA Cup tie against non-league Dover Athletic.

He was called up to the senior Republic of Ireland squad in October 2005,[41] making his full international debut against Sweden at Lansdowne Road on 1 March 2006.

During 2010 World Cup qualifying, Doyle established himself as Robbie Keane's ideal strike partner in the national team's attacking quartet that included Damien Duff and Aiden McGeady.

In the absence of Robbie Keane, Shay Given and other players who had been allowed to return to their clubs, Doyle captained Ireland for the first time in a friendly against South Africa on 8 September 2009.

[58] Towards the end of the Trapattoni era, Doyle fell out of favour and was dropped from the squads but he was recalled by Interim manager Noel King for the qualifiers against Germany and Kazakhstan.

[63] Doyle was part of RTÉ Sport's punditry team for the UEFA Euro 2020, alongside Damien Duff, Liam Brady and Richie Sadlier.