The Golkar Party, which came in second in the April 9 general election, has agreed to form a coalition with the People's Conscience (Hanura) Party to back Golkar chairman Aburizal Bakrie's presidential bid.
"We have reached common understanding," Mr Bakrie told reporters on Tuesday afternoon.
The move is expected to strengthen Mr Bakrie's chances of securing the nomination, and comes a day after Golkar advisory board chair Akbar Tandung said on Sunday that Mr Bakrie's nomination was not a done deal, and that it had to be discussed by party leaders at their upcoming meeting in May.
Mr Akbar cited concern over the party's lower-than-expected performance on April 9, where it got only 15 per cent of the popular vote according to a quick count by pollster Saiful Mujani-LSI, and an estimated 96 seats.
The Straits Times understands that leaders from Golkar and Hanura agreed to form a coalition for the July 9 presidential election on Sunday night.
Both parties have yet to get official endorsement for the deal, but it is expected to strengthen Mr Bakrie's position at the Golkar board meeting in May.
Hanura, led by former armed forces commander and former Golkar member Wiranto, won 5.1 per cent of the popular vote, the lowest among the 10 parties that made it to the incoming Parliament.
It is expected to get between 17 and 28 seats, that combined with Gokar's share, will barely take the combined total of both parties past the 112-seat requirement needed to field a presidential pairing.
It is however not clear for the moment who will be Mr Bakrie's running mate for vice-president.