[6] He began his career playing in Wimbledon's youth system,[7] but he joined non-League club Welling United in 1993 after being released at the age of 16.

Finnan turned professional when he signed with Birmingham City in 1995, who paid a fee of £100,000 to Welling United to acquire his services.

[10][11] He appeared in all of Notts' games for the remainder of the season,[11] helping the team finish fourth in the Second Division and qualify for the promotion play-offs.

[18] After strong showings for Notts County in the 1997–98 season, Fulham manager Kevin Keegan paid £600,000 for his services in November 1998.

[29] By April 2003 with few games to go, Fulham were close to the relegation zone but picked up 10 points out of a possible 15 to stay in the top-flight, finishing in 14th position.

[36] Finnan's goal against WBA meant that he became only the second player to score in each of the five highest divisions of English football; the first was Jimmy Willis.

[39] Finnan played for Liverpool as first-choice right-back for the 2006–07 season despite heavy competition from newly arrived teammate Álvaro Arbeloa.

[45][46][47] In the summer of 2008, after the arrival of fullback Philipp Degen at the club from Borussia Dortmund, Finnan was linked with a move away from Anfield.

[48] He was offered by Liverpool as a makeweight in a deal to sign Gareth Barry from Aston Villa; the player accepted the move but the clubs were unable to agree a fee.

[50] On transfer deadline day, 1 September 2008, Finnan signed a two-year deal with La Liga club Espanyol for an undisclosed fee.

[51] Injuries limited his first team appearances,[52] and rumours of a return to the Premier League in the January 2009 transfer window with Arsenal or Tottenham Hotspur were dismissed by Espanyol's sports director Paco Herrera and by coach Mané, who considered him an important member of the team.

He cemented his place in the Irish starting XI during the 2002 World Cup qualification matches, supplying the cross for Jason McAteer to score the only goal in a crucial 1–0 home win against the Netherlands in September 2001.

Finnan appeared in all three of Ireland's group E games in the 2002 FIFA World Cup against Cameroon, Germany and Saudi Arabia.

[61] Tempted by the prospect of working with the newly appointed Ireland manager Giovanni Trapattoni,[62] Finnan came out of retirement in August 2008 to be included in the squad to face Norway in an international friendly.