The former telecommunications tycoon, premier from 2001 until he was ousted in a 2006 coup, lives in self-imposed exile after fleeing Thailand to avoid a jail sentence for graft in 2008.
He would still be subject to jail upon return.
In a social media post on Saturday, Thaksin's youngest daughter, Paetongtarn Shinawatra, said she would meet her father at Bangkok's Don Muang Airport on "Tuesday, August 22".
Also scheduled for Tuesday is another parliamentary vote for prime minister, to be nominated by the Thaksin-backed Pheu Thai Party.
Thaksin earlier postponed his return from August 10, citing the need for a medical check-up.
He still faces up to 10 years in jail.
The 74-year-old would be subject to the judicial process upon his return, deputy national police chief Surachate Hakparn has said.
Some analysts said Thaksin's return suggests Pheu Thai has reached a deal with political parties on forming a government after gaining support from military-backed parties.
"Thaksin's return on voting day shows that he is confident that Pheu Thai's prime ministerial candidate will be elected in one round," said Thanaporn Sriyakul, chair of the Political Science Association of Kasetsart University.
The second-placed Pheu Thai this month took over efforts to form a government after the leader of the election-winning Move Forward party failed in his bid to become prime minister.
Pheu Thai, set to nominate real estate tycoon Srettha Thavisin, needs the support of more than half the bicameral legislature, including the military-appointed Senate.
The party on Thursday gained support from a rival military-backed party after an MP from another military-backed party said they would support Pheu Thai in overcoming the impasse.
