Widodo, who won legions of fans during his time as Jakarta governor, started the campaign period with a ceremony at his Indonesian Democratic Party of Struggle's headquarters in the capital.
The party head handed him a cone of rice, a traditional gift in Indonesian culture to mark important events. He was due to set off in the evening to the eastern region of Papua, his first stop on a mammoth tour round the archipelago to win votes for the July 9 poll.
His only opponent, ex-general Prabowo Subianto, was heading to Bandung, in the west of the main island of Java, to begin campaigning later Wednesday.
Voters face a stark choice between Widodo, seen as a fresh face in a country still dominated by figures from the three-decade Suharto dictatorship, and Prabowo, who has deep roots in the past.
Widodo has enjoyed a a meteoric rise, from small town mayor on Java, to Jakarta governor, and now the likely next president of Indonesia.
The 52-year-old's humble background and common touch - he regularly tours the sprawling city's slums in casual clothes - has made him popular in a country where leaders have typically come from the ranks of the military or wealthy, aloof elites.
"I will vote for Jokowi as he is humble and close to ordinary people," said Suradi, 60, a motorised rickshaw driver in the capital who like many Indonesians goes by one name.
In contrast, Prabowo was a leading figure in the military who commanded the army's special forces in the dying days of the Suharto era in the late 1990s and has admitted ordering the abduction of democracy activists.
But rights issues have taken a back seat in the local media's coverage of the elections, and Prabowo has played up his military background in a country where many have a yearning for a strong leader.
Despite Widodo's huge popularity - he has been leading in surveys to become Indonesia's next leader for months - Prabowo has narrowed the gap dramatically since legislative polls in April, while Widodo has lost ground.
Some 186 million people are eligible to vote in the election across the sprawling Indonesian archipelago, which is the fourth most populous country on Earth and home to the world's biggest Muslim population.