Born in Manresa in October 1961, Manuel Estiarte began playing water polo in his home town before moving to Barcelona to sign for Barcelona Swimming Club when he finished his studies. He was a European Cup semi-finalist with them, and went on to win this competition in 1981, also lifting the European Super Cup that same year. He scored over 600 goals for Barcelona Swimming Club, winning the Spanish league with them four times. He signed for Pescara in 1984 and went to play in Italy, where he won ten League and Cup medals in all. He also twice won the European Cup Winners' Cup with Pescara, as well as the LEN Trophy in 1996, leading to a water polo 'Grand Slam' of four European championships, something that had never before been achieved.

In 1980, he and the Spanish team were fourth at the Moscow Olympics, where he was the revelation of the tournament, scoring 21 goals in 8 games, becoming the Games' leading scorer, just as he also was at the Los Angeles and the Seoul Games. Besides fourth place in Moscow, he was also fourth in Los Angeles (1984), and silver medallist in Barcelona (1992), before achieving his greatest ambition, an Olympic gold medal at Atlanta (1996).

He was runner-up with the Spanish national team at Perth (1991) and Rome (1994) and in the European Championships was runner-up in Athens (1991) and twice third, in Rome (1983) and Sheffield (1993); he has also been third twice in the World Cup, in Duisberg (1995) and Barcelona (1991). He has won the Italian league with his present club four times. In 1998 he was World Champion, and runner-up in the European club league. Following his retirement after the Sydney Games he was a member of the International Olympic Committee Athletes´s Commission until 2004.