It is described as a shock loss for Chile's right-wing coalition.
In this weekend's election, the governing parties only managed to gather 38 of a total of 155 seats for the assembly that will write the country's new constitution.
- The people have sent a powerful signal to us, both to the government and the traditional political parties.
We do not live up to the expectations of the Chileans, Sebastian Pinera said in a speech during the night until Monday after admitting defeat.
It will be difficult to stop major reforms
The defeat means that they missed by a margin the goal of getting at least a third of the votes.
The governing parties are finding it much more difficult to stop major reforms of the new constitution that will replace dictator Augusto Pinochet's 40-year-old constitution.
The current law, which is based on a comprehensive market-liberal model, was the basis for the major protests in the country in 2019 against what is considered social injustice and for basic welfare.
Chile today has the largest economic inequality within the OECD.
According to estimates, one percent of the country's population owns more than a third of its assets.
Referendum no later than 2022
The final delegation will consist of half men and half women.
17 of the seats have been earmarked for representatives of Chile's indigenous peoples and the system is based on a proportionate division of groups of independents as well as people supported by political parties.
The Assembly now has one year to draw up a proposal for a new constitution which will form the basis for a final referendum.