A self-described social Christian, Ossandón has been focused during all his years as a politician fighting for poverty reduction and for increasing the quality of life of Chileans.

[3][4] By the time he turned 30, he decided to run for mayor in the rural town of Pirque, a suburb of Santiago.

[citation needed] He ran for president in 2017, obtaining 27,6% in the presidential primaries (Sebastian Piñera won the candidacy with 57,5% of the vote).

Ossandón has established a reputation as a leading progressive voice on issues such as campaign finance reform and combating political and business corruption.

[6][7] An opponent of same-sex marriage, he criticized President Sebastián Piñera for pushing the bill legalizing it in the Chilean Congress, calling it a "low blow, it was a tremendous stab for many people who have a more conservative position, just before entering into an election, which was not necessary.