Fierro began his career at Chilean giants Colo-Colo, being promoted to first-adult team in 2002. Along the seasons, he break into the first team and then he became an undisputed player with Claudio Borghi with whom won four league titles and reached a 2006 Copa Sudamericana runner-up, all of active way.
On 26 August 2008, Fierro joined Brazilian powerhouse Flamengo becoming the first Chilean player on join the club.[1][2] Nevertheless, he only completed eight league games in his debut season. In 2009, Fierro had a more active role in the team after being chosen to replace Ibson who left the club on loan,[3] playing 24 games and scoring one goal against 2008 Série A defending champions São Paulo in a 1–1 away draw.[4][5][6] That season he helped Flamengo to win the Brasileirão.
On 15 July 2010, was reported that Fierro joined Boca Juniors in an alleged request of Claudio Borghi to the club board.[7] However a serious injury stopped his incorporation and on 17 August it was confirmed that he left the club for return to Rio de Janeiro with Flamengo and start his recuperation.[8]
In 2012, Fierro returned to Colo-Colo. Following Pablo Contreras departure, he became the club's captain and in 2014 he was part of the Torneo Clausura team champion, where he was an undisputed player.
In July 2021, he announced his retirement from the football activity at the age of 38.[9]
International career
In 2006, he received his first international cap and debuted against Colombia on 16 August. The following year he was included in Chile's squad for the 2007 Copa América. On 30 January 2008, he scored his first international goal during a game against South Korea where scored the only one goal of the game in a 1–0 win over the Asians.
Both Fierro, whose second last name is Caniullán, and his wife are of Mapuche descent. Due to this, as the Colo-Colo team captain he used to wear an armband with Mapuche motif.[10]
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