Left-wing candidate Michelle Bachelet was expected to win the majority against Evelyn Matthei, a former minister in the ruling center-right coalition, the BBC reported.
Bachelet, 62, won 47 percent of the first round of voting on Nov. 17, while Matthei, 60, took 25 percent.
Matthei entered the race after two members of her party resigned earlier this year. She has argued for a continuation of the policies of outgoing President Sebastian Pinera, stating she believes Chileans are "better off" now than they were before he was elected
Bachelet served as the president of Chile from 2006 through 2010, but was constitutionally banned from seeking a second term. She has stated that she wishes to increase taxes in Chile in order to offer free university education and reform political and economic structures.
Polls opened at 8 a.m. local time, and will remain open for 10 hours