Bachelet, who became Chile's first woman president on her election in 2006, declared her intentions in the Santiago neighborhood where she spent her childhood, The Santiago Times reported Wednesday.
She completed her term in 2010 and resigned as head of the United Nations agency U.N. Women this month.
"I told you before that we would talk [about my candidacy] in March," she told a gathering at a photography exhibit devoted to her term as president. "And here I am, ready to fulfill this challenge. I have made the decision to be a candidate."
A recent poll found Bachelet 28 points ahead of her closest rival for the presidency, conservative former Public Works Minister Laurence Golborne.
Chile's current president, Sebastian Pinera, is prohibited by the country's Constitution from seeking a second consecutive term.
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