Yingluck Shinawatra, sister of former prime minister Thaksin Shinawatra,has notified the Pheu Thai Party about her intention to become a party-list candidate.
Yingluck visited the party on Tuesday to complete her candidacy declaration.
Pheu Thai spokesman Prompong Nopparit said his party will likely unveil its candidate for the position of prime minister by tomorrow.
Prompong and a large number of Pheu Thai MPs hinted that Thaksin had already finalised his decision to endorse Yingluck for the top job.
Yingluck is expected fill the number one slot in the Phue Thai Party list, followed by former Puea Pandin faction leader Pracha Phromnok.
The top ten candidates in the Phue Thai list would include Chalerm Yoobamrung.