Dacourt made his debut match in Division 1 with Strasbourg on 20 March 1993 in an away game with Auxerre, which Strasbourg lost 2–0. On 24 May 1997, he scored his first Ligue 1 goal for Strasbourg in an away match against Paris Saint-Germain, however, Strasbourg lost the match 2–1.
Dacourt transferred to Everton in 1998 and his debut game in the Premier League was a 0–0 draw against Aston Villa on 15 August 1998. On 17 February 1999, he scored his first goal in the 5–0 victory against Middlesbrough. Dacourt became a fan favourite with the Everton supporters, but was booed at the club's final home game of the season in May 1999 against West Ham after comments in a French article that he was unhappy at the club and looking to leave in the summer.
Dacourt returned to France after one season at Everton playing for RC Lens, where he impressed and earned a multimillion-pound move back to the Premier League to the Yorkshire club Leeds United.
Dacourt joined Leeds United from Lens in a £7.2 million move in 2000, and broke Leeds' transfer record at the time. He proved to be an instant hero at Elland Road with his tenacious style and ball winning play. His time at Leeds saw them reach the Champions League semi finals and also finishing in the top 4 of the Premier League. He was a regular in centre midfield under manager David O'Leary, mainly partnering David Batty at the heart of Leeds' midfield. His form at Leeds also saw Dacourt become a regular for the French national side. But after the sacking of O'Leary, his replacement Terry Venables dropped Dacourt from the Leeds team and favoured players like Paul Okon ahead of him in the pecking order.
Venables had a public falling out with Dacourt, in which Venables claimed he 'would personally drive Dacourt' away from the club. With Leeds' financial problems Dacourt was loaned out to A.S. Roma, and during his time out on loan Venables was sacked and replaced by Peter Reid with many believing Dacourt would return, but during the summer his loan move to Roma was made permanent. Dacourt proclaimed that he would like to return to Leeds one day in the future after playing in his former teammate Lucas Radebe's testimonial.
Dacourt joined A.S. Roma on loan, with an option to purchase for £4 million. He signed a contract worth €1.85 million in gross. On 10 July 2003 Roma agreed to sign Dacourt outright for a new price: €5 million. Dacourt signed a 3-year contract, worth €4 million in gross each season. After being on the losing side in the Coppa Italia final against Internazionale in 2005–06, Dacourt joined the club from Roma on a two-year contract in accordance with the Bosman ruling.
Originally signed as a backup player for Internazionale, he became a key player of the league victory, in light of all the injuries to Patrick Vieira. On 2 December 2007, against Fiorentina, he damaged his left knee, with a torn cruciate ligament and damage to two other ligaments in it. He was expected to be out for the rest of the 2007–08 season.
In the 2008–09 season after recovering from injury, Dacourt did not feature as regularly and was not in Inter manager José Mourinho's plans.
On 2 February 2009 he joined English side Fulham on loan until the end of the 2008–2009 season after being signed by Roy Hodgson. However, he had to settle for being confined to mainly substitute appearances due to the impressive form of Fulham's midfield and also Dacourt picking up some injury niggles, Dacourt's move to Fulham was not made permanent come the summer, Dacourt briefly returned to Internazionale where his contract then expired and he became a free agent.
Dacourt signed a one-year contract with Standard de Liège on 23 September 2009. He was brought in to replace Steven Defour who had an injury on his foot and should be inactive for three months, Defour was the central midfield partner to Axel Witsel. On 8 February 2010 Standard de Liège declared the end of his contract.
Dacourt played for France in the 1996 Olympic Games.
After impressing for Leeds United, his first senior appearance with the national team came against hosts South Korea in a match in the FIFA Confederations Cup in 2001, which France won 0–5, as they went on to win the tournament. He was a member of the French team that won the 2003 FIFA Confederations Cup and also appeared in the 2004 European Championship.Strasbourg
UEFA Intertoto Cup: 1995
Coupe de la Ligue: 1996–97
Serie A: 2006–07, 2007–08
Supercoppa Italiana: 2006
FIFA Confederations Cup: 2001, 2003