Communist Jeannette Jara leads right-wing politician José Antonio Kast, conservative Evelyn Matthei and far-right Johannes Kaiser in the polls.
However, the former labour minister Jara is unlikely to win an absolute majority, meaning a run-off election between the top two candidates in December will probably be necessary.
A victory for a right-wing candidate in the run-off is seen as probable if defeated rivals can unite.
In addition to the new president, almost half of senators and all 155 members of the Chamber of Deputies are up for election on Sunday.
The election campaign in the South American country has focused on economic issues, crime and migration.
Although Chile is still one of the safest countries in the region, crime has recently increased in some areas.
Incumbent left-wing president Boric is not allowed to run again after his four-year term for constitutional reasons.
About 15.8 million people are eligible to vote on Sunday, with results expected late in the night. Voting is compulsory in Chile.
The future head of state is to take office on March 11, 2026.
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