By Clinton Porteous
BBC News, Santiago
A Chilean woman has been declared the sole presidential candidate for the ruling centre-left coalition.
Ms Bachelet is the only candidate put forward by the ruling coalition
Michelle Bachelet is a member of the Chilean Socialist party.
The powerful Democratic Christian party endorsed her two months after its own candidate dropped out of a historic primary contest between two women.
The coalition, known as the Concertacion, has held office for the past 15 years since General Augusto Pinochet left power.
Ms Bachelet told more than 500 delegates from the Democratic Christian party that together they would march to victory.
She singled out for special praise the former Foreign Minister, Soledad Alvear, a member of the Democratic Christian party who dropped out of the primary race in late May.
Since then, there have been tense negotiations over the role of her party if Miss Bachelet makes history and wins in December.
Chile has never had a female leader, but Miss Bachelet would break political tradition in other way if she wins.
She is a single mother and viewed as more left-wing than the current president, Ricardo Lagos, who is a member of the Socialist party.
Miss Bachelet's main rivals are both men: Sebastian Pinera and Joaquin Lavin from the two major conservative parties.