His opponent, Prabowo Subianto, has asked Widodo to wait for the official results.
An unofficial preliminary tally on Wednesday showed Widodo slightly ahead of Prabowo.
"Today, Indonesia's new son has been chosen by the people," Widodo, governor of Jakarta, declared. "We begin a new phase in our history and we start a new beginning of Indonesia."
Although the final tally isn't yet available, quick count polls in Indonesia tend to be accurate within a 1-2 percent margin of error.
Prabowo urged patience, telling his supporters to "allow KPU (Indonesia's election commission) to work and decide the victory."