Joko Widodo, who has become a hugely popular figure during his time as Jakarta governor due to his common touch, has selected Jusuf Kalla, 72, as his vice presidential candidate, the official said.
Analysts say picking a veteran politician is a wise move. While Widodo, 52, has been hailed for being a break from previous leaders with deep roots in the autocratic Suharto era, he has never had a role in national politics.
Widodo, known universally by his nickname of "Jokowi", was expected to officially announce Kalla as his running mate later today.
Kalla, a wealthy businessman, was vice president during President Susilo Bambang Yudhoyono's first term in office, from 2004 to 2009.
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He has argued that he was a key actor behind many of the achievements of this period, from the fight against corruption to a reduction in deadly attacks by Islamist militants.
"Kalla is also a popular figure."
Widodo has been a political phenomenon since being elected Jakarta governor in 2012 and the presidential poll on July 9 is seen as his to lose. He has temporarily stepped aside from his post as governor to contest the election.
He rose to prominence after serving as mayor of a small town on the main island of Java and has won many admirers with his down-to-earth style. He makes regular tours of Jakarta's slums in a casual shirt and jeans.
Widodo maintains a strong lead in opinion polls although his hopes of an easy ride to the presidency were dealt a blow at legislative elections in April, which set the stage for the presidential polls.
His PDI-P did not do as well as expected, meaning the party has had to form a larger coalition than it might have liked to put Widodo forward for the presidential polls.