He began his career as a youth team player at Manchester United in 1995, turning professional in 1999, but signed for Preston North End two years later after a short loan spell.

He helped the club to the SPL title in 2010–11 and also played in the 2011 League Cup final victory, before departing at the end of the 2011–12 season, when his contract expired.

In addition to these clubs, he has also played for Port Vale, Norwich City, Ipswich Town, and Doncaster Rovers on loan.

He began his management career with Linfield in October 2015 and led the club to a NIFL Premiership, Irish Cup and County Antrim Shield treble in 2016–17.

Healy was born and raised in Killyleagh, Northern Ireland, and played for Crossgar, Lisburn Youth and Down Academy High School in Downpatrick.

He made his debut for the reserve team in April 1998, coming on as a substitute for Ole Gunnar Solskjær in a 2–0 win over Birmingham City.

He made his competitive senior debut for United on 13 October 1999, coming on for Danny Higginbotham in the 66th minute of a 3–0 away defeat to Aston Villa in the League Cup.

In 2000–01, Healy was included in the Manchester United squad for their Champions League second group stage match against Panathinaikos on 21 November 2000.

[7] A permanent move was completed on 3 January 2001, as Preston paid Manchester United a fee of £1.5 million, before Healy signed a four-and-a-half-year contract.

[8][9][10] Healy made his debut for Preston against Sheffield United on 30 December 2000; he scored after just four minutes in the 3−2 loss at Bramall Lane.

Healy reunited with former Northern Ireland boss Lawrie Sanchez at Fulham in July 2007 for a reported fee of around £1.5 million.

[15] He scored his first goal for Fulham in a pre-season friendly against South China in the Asia Trophy, with a low diving header.

Following the sacking of Sanchez, new manager Roy Hodgson preferred a strike partnership of the American pairing of Brian McBride and Eddie Johnson, leaving Healy on the bench.

[16] In July 2008, Healy caused controversy when he adopted the posture of a flute player (similar to a previous incident involving Paul Gascoigne) in response to a question posed by Celtic fans chanting, "Where were you on the Twelfth?"

[17] He remained out of favour with Roy Hodgson, who regarded his signings Andy Johnson and Bobby Zamora ahead of Healy in the pecking order.

Healy made his debut for Sunderland four days later in the League Cup and marked by scoring the winning goal in extra time against Nottingham Forest.

[22] He made his debut against Middlesbrough on 6 February 2010, helping Ipswich to earn a point by setting up Murphy to score with a cross.

[24] Healy joined Doncaster Rovers on loan in November 2010, to fill the void left by the injured Billy Sharp.

[37] He made a scoring debut for the "Shakers" on 25 August, converting a penalty in a 2–2 draw with Coventry City at the Ricoh Arena.

[39] Unable to find a club after his release and struggling with persistent ankle injuries, Healy announced his retirement from football on 3 December 2013.

On 6 June 2004, in a friendly game away to Trinidad and Tobago (his 35th international), he scored his 13th and 14th goals for Northern Ireland, thus equalling and overtaking Colin Clarke's record for the country.

[46] On 7 September 2005, at Windsor Park, Healy secured a famous victory for his country against England in a World Cup qualifier when he scored the only goal of the game.

[11] A month later, on 6 September 2006, Healy became the first man since Colin Clarke to score a hat-trick for Northern Ireland and the first since George Best to do so in Belfast.

[48] He scored both of Northern Ireland's goals in a 2–1 win against Sweden on 28 March 2007,[49] and two more against Liechtenstein on 22 August, followed by a penalty away to Iceland on 12 September.

Healy's comments were interpreted by some Scottish and Irish Catholics as a reference to Rangers fans' chant – "'the famine is over, why don't you go home?"

"[51] Despite finding a new club, Healy was left out of the Northern Ireland squad for the 2014 FIFA World Cup qualifiers in 2012 by new manager Michael O'Neill.

[60] Despite this setback, the "Blues" went on to win the league title in 2016–17, and ended the campaign with a treble after beating Coleraine 3–0 in the final of the Irish Cup.

[67] The 2019–20 season was ended early due to the COVID-19 pandemic in Northern Ireland, and Linfield were crowned champions after finishing ahead of Coleraine on points per game.

[73] Despite securing a fourth consecutive title at the end of the 2021–22 season, Healy stated that he had "never quite won the supporters over" and that online abuse was starting to affect his family.

[76] Linfield came close to becoming the first Northern Irish team to qualify for the group stages of European competition when they took FK RFS of Latvia to a penalty shoot-out in the play-offs for the UEFA Europa Conference League on 25 August 2022.