Born in Santiago, Orellana began his career in Colo-Colo and then moved to Audax Italiano. He made his Primera División debut at only 18, and scored 12 league goals in 38 games in the 2007 season as his team finished third in the Apertura, won their Clausura group and reached the semi-finals in the play-offs.

Orellana made his debut for Chile in 2008. On 15 October of the same year he scored his first international goal, in a 2010 FIFA World Cup qualifier against Argentina in Santiago (1–0 win).

Orellana played in the 2008 Toulon Tournament with the under-20s, helping them to the second position.

Orellana signed with Udinese Calcio in Italy on 23 May 2009, for €3.2 million, being immediately loaned to Xerez CD in the Spanish Segunda División. In the following campaign he continued in that country and tier, joining Granada CF also in a temporary deal and being a solid contributor as the Andalusians returned to La Liga after a 35-year absence, netting seven goals – plus one in the play-offs– in 2,673 minutes of play (he was also sent off three times).

On 10 October 2009, for the same competition, Orellana closed the scoring in a 4–2 win in Colombia, securing the national team’s qualification to the World Cup after 12 years. In the final stages in South Africa, he came on as a substitute for Alexis Sánchez midway through the second half of a 1–2 group stage defeat against eventual champions Spain.

Orellana was acquired for good by the Galicians in early January 2013. On 5 April 2015, he was sent off in the dying minutes of a 0–1 home loss to FC Barcelona for throwing a piece of turf at Sergio Busquets’ face.

On 31 January 2017, after a serious run-in with manager Eduardo Berizzo, Orellana signed a four-month loan with fellow league side Valencia CF, with the possibility of making the move permanent until June 2018 at the end of the campaign.

After this happened, Orellana was completely ostracised by new manager Marcelino García Toral, and on 1 December 2017 he moved to SD Eibar also of the Spanish top tier on loan until the following 30 June. The following April, immediately after the Basques confirmed their survival, a permanent €2 million contract was agreed after the pertinent clause was triggered; he scored eight goals in 2019–20 and also provided more assists than anyone in the squad, as they again managed to stay afloat.

On 20 July 2020, Real Valladolid announced Orellana had joined them on a two-year deal.