Pheu Thai, which backed ousted premier Yingluck Shinawatra, voted in stalwart Viroj Pao-in as party leader, members said in a briefing to the media.
Viroj has "worked hard during the party's difficult times", said Pheu Thai stalwart Sudarat Keyuraphan, who was made head of the strategic committee, Presstv Reported.
The junta, which seized power and toppled Yingluck's administration in a coup in 2014, has postponed elections multiple times since taking over but has insisted the vote will now go ahead in February.
Parties are still under a partial political ban, which bars them from campaigning or holding rallies.
It remains to be seen whether Pheu Thai can capitalize on previous successes at the ballot without the star power of Yingluck and her older brother Thaksin, who was himself pushed out in a military takeover in 2006.
The siblings live in self-exile to avoid what they say are politically motivated court charges.
The wealthy and powerful Shinawatra clan has won every election since 2001 through populist platforms and welfare schemes that have angered Bangkok's military-aligned elite.
But large sections of society have grown weary of military rule and endemic inequality while protests have bubbled up in recent months calling for a return to democracy.
"People vote for us not because of the party's name or how we look like but... (but) because we can fix their problems," Sudarat said. "So we are confident about the success in the upcoming elections."
She declined to reveal who the party will put up as candidate for prime minister. Even if elections are held a return to full-fledged democracy in Thailand is unlikely, analysts say.
The constitution written by the junta calls for an upper house whose members are appointed, and includes other checks on the power of future civilian governments.
Despite insisting he has no interest in politics, Thailand's junta leader Prayut Chan-O-Cha has also been hinting at a possible run, with campaign-style stops across the country and a stepped-up social media profile.