[3] Nicknamed Gringo,[4][5] he made a name for himself at Paris Saint-Germain, moving in 2004 to Manchester United and subsequently to Real Madrid, winning three trophies in total with the latter two clubs.

[8][9] He began his career in his home country with Newell's Old Boys and, following attention from various European clubs, the 19-year-old signed for Real Valladolid in Spain, not managing one single La Liga appearance in his first season and also being loaned to Sporting CP in December 1998.

[8] He marked his debut on 11 September with a goal in a 2–2 away draw against Bolton Wanderers,[11] and immediately established himself as first-choice left-back, being regularly lauded by fans with the chant of "Ar-gen-tina!

[15] He made a comeback with the reserve team in April 2006, but a minor injury picked up in his third game back prevented him from making a first-team appearance before the end of the season.

Heinze returned to action for United in 2006–07, and eventually won a place in the side back as a central defender, due to an injury crisis.

[17] After becoming disillusioned with manager Alex Ferguson by his lack of regular first-team action,[18] Heinze demanded a transfer to Liverpool during the close season.

[25] In his first year he scored a career-best four league goals in 27 matches, as L'OM won both the national championship and the season's Coupe de la Ligue.

On 27 March 2010 he was a starter as his team defeated Bordeaux in the latter competition's final, for Marseille's first major title since 1993;[26] on 5 May, he netted the opener in a 3–1 home win against Rennes, which clinched the league.

[39] Heinze participated in the 2007 Copa América, scoring with his head from a Juan Román Riquelme free kick in the semi-finals against Mexico, a 3–0 win for the eventual runners-up.

[40] In the 2010 FIFA World Cup he played in four of Argentina's five matches in South Africa, netting the game's only goal – his third international – in a group stage victory over Nigeria.

[52] Heinze banished Atlanta's star striker Josef Martínez from training, and publicly said that this was his own decision, rather than a precaution based on the Venezuelan's COVID-19 diagnosis at the 2021 Copa América.

In 2005, he signed an endorsement with Puma AG in which at least a million dollars was paid to him over a period of five years through an account in his mother's name in the British Virgin Islands.