The governor's populist style has won him wide popularly in the world's third biggest democracy, whose years of rapid economic growth have started to slow, threatening to further widen the gulf between the rich and the growing ranks of poor.
But the election is not yet won and one recent poll showed Jokowi's lead had narrowed slightly, although he was still 15 points ahead of his closest rival, ex-general Prabowo Subianto.
The winner of July's presidential election needs a simple majority. Failure to do so would force a run-off in September with the new government taking office the following month.
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Jokowi told reporters the agreement with Golkar did not mean any deal had been cut on his running mate.
"Them (Bakrie and Jokowi) standing together in that market is a symbol that the coalition is happening," senior Golkar official David Tampubolon told Reuters.
"We will make another announcement about the official coalition after our (party meeting) on May 17."
Media speculation has tipped former vice-president Jusuf Kalla, a Golkar member who remains a popular figure and currently heads the Indonesian Red Cross.
Golkar managed to survive Suharto's downfall in 1998, repair its image and strengthen is grass roots support. It is seen as strongly pro-business.
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"(Golkar's) strength is organisation and money ... If in addition there is a prominent Golkar figure who becomes VP, that would be an even bigger boost," said Douglas Ramage, Jakarta-based political analyst.
The announcement came shortly after Jokowi's main rival Prabowo announced he had chosen chief economic minister Hatta Rajasa as his running mate. Rajasa heads the moderate Islamic PAN party.
The announcements remove two potential candidates - Rajasa and Bakrie - for the presidency and turn the July election largely into a contest between Jokowi and Prabowo.