Pinera, who led Chile from 2010-2014, had gone back to his business empire. Chilean law does not allow immediate re-election.
"Before you and all my fellow citizens, I am announcing my decision to seek the presidency again," he said at a rally in a Santiago park.
"The only reason that I am here, standing again for the presidency, today, is because I want to give the best of myself."
It will be his third go at the presidency. In 2005, he lost to socialist (current President) Michelle Bachelet. In 2009, he ran and won, becoming the first elected conservative since the end of the 1973-1990 Augusto Pinochet dictatorship.
At the moment, polls show Pinera with support of about 25 percent ahead of the November 19 election.
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