During Pizarro's stay in Italian football, he won one Serie A title (2005–06), three Coppa Italia titles and two Supercoppa Italiana titles. His Italian nickname is "Pek", diminutive of "pequeño", meaning "small" in Spanish, because of his short height (1.68 meters).
He plays for the Chile national team, for which he won the Bronze medal at 2000 Summer Olympics, and played at two Copa América. He made his full debut in 1999, playing at that year's Copa América, and was part of the Chilean squad which won its first ever tournament in 2015.
Pizarro started his career at Santiago Wanderers in his homeland Valparaíso. After a season playing at Seaport Team since his promotion to first-adult team in 1997, he was transferred to Italy’s Udinese Calcio of the Serie A. In 2001, he was loaned to Chilean powerhouse Universidad de Chile for gain experience. Once back in Friuli he settled as the team starter central midfielder, performing well during his five seasons there.
On 14 July 2005, Pizarro was transferred to F.C. Internazionale Milano for a reported fee of €10 million (plus half of Goran Pandev rights, which Lazio bought a year later for €4m) on a four-year deal. There, not repeating his successful campaigns at Udinese and being overshadowed Argentine star Juan Sebastián Verón, won a league title, a Coppa Italia and a Supercoppa Italiana.
On 19 August 2006, A.S. Roma acquired Pizarro's 50% transfer rights, agreeing a €6.5 million transfer fee on a four year co-ownership deal. On his arrival he chose the number 7 shirt and reunited with Udinese Calcio coach Luciano Spalletti.
On 12 September 2006, Pizarro scored his first competitive goal for the club in a 4–0 Champions League victory over Shaktar Donetsk at 89th minute. Five days later, he netted twice in a 3–1 Serie A win over AC Siena. He helped Roma win the 2006–07 Coppa Italia title where was one of the team top-scorers with three goals. On 20 June 2007, Roma announced that they paid Inter the remaining 50% of Pizarro's rights to keep him at the Rome–based team until 2010. The next season, he was an undisputed starter with Daniele De Rossi in midfield, making over thirty league appearances as well as in the UEFA Champions League where he scored a goal in a 2–1 win over Real Madrid to seal the team’s advance to the quarterfinals. Nevertheless, during the season Pizarro once again won the Coppa Italia.
In October 2009, Pizarro signed another contract extension that originally would keep him at the club until June 2013. He finished the 2009–10 season with two goals and eight assists in 31 appearances, helping Roma finish second in Serie A behind eventual winners Inter.
Pizarro signed on loan for Manchester City from Roma on 31 January 2012 until the end of the season, where manager Roberto Mancini had previously managed Pizarro at Inter Milan. He made his debut four days later as an added-time substitute for Adam Johnson in City's 3–0 win against Fulham, becoming the first Chilean to play for Manchester City. On 22 February, he came off the bench to score and had an assist against Porto in the Europa League as City won 4–0 in the second leg of the tie, having won 2–1 in the away leg.
On 13 May 2012, Manchester City were crowned Premier League champions for the 2011–12 season after beating Queens Park Rangers 3–2. Pizarro made five league appearances that season, which was not enough for a medal. Pizzaro loan spell with Manchester City came to an end and returned to Roma, where he vowed not to move again.
On 9 August 2012, Pizarro transferred to Fiorentina and signed a two-year deal with the club. Pizarro played 83 times for Fiorentina, and scored four goals.
He was an unused substitute in the 2014 Coppa Italia Final, which Fiorentina lost 3–1 to Napoli.
He decided to return to Chile with Santiago Wanderers on a two-year contract.
Pizarro began his international career in 1999. After being one of the best players of the South American Youth Championship that year, Chile manager Nelson Acosta gave him an opportunity in the senior team.
He played in the 1999 Copa America and also the 2000 Summer Olympics, where he won the bronze medal. He also participated in the 2002 and 2006 World Cup qualifiers, with Chile failing to qualify on both occasions.
After failing to qualifying for the 2006 FIFA World Cup in Germany, Pizarro announced his retirement from international football, listing several reasons for his decision. He disliked ex-coach Juvenal Olmos and ex-association president Reinaldo Sánchez. Also, he believed the players on the national team played solely to gain popularity. He also said he wished to spend more time with his family.
On 20 May 2013 he was called up to the national team for the 2014 World Cup qualifiers, returning to the Chile national squad after having meetings with head coach Jorge Sampaoli. Thus ending an eight-year absence from international football. Then after failing to be named in Chile’s list of 23 for the World Cup, he was part of 2015 Copa América historical champions team.Inter Milan
Supercoppa Italiana: 2005
Serie A: 2005–06
Coppa Italia: 2005–06
Supercoppa Italiana: 2007
Coppa Italia: 2006–07, 2007–08
Premier League: 2011–12
Universidad de Chile
Chilean Primera División: 2016–17 Clausura
Olympic Games Bronze Medal: 2000
Copa America: 2015