Thaksin Shinawatra has shown confidence Pheu Thai would again make a comeback in the next election after the party was unseated by the coup, led by then army chief Gen Prayut Chan-o-cha.
The former fugitive prime minister said on his birthday on Thursday that the National Council for Peace and Order's attempts to hold on to power were alienating its support and turned the odds in favour of the party he was backing.
People in Thailand are suffering due to the higher cost of living when their income remained unchanged, he said.
"They [the NCPO] will lose badly because they don't understand the hearts of people," said Thaksin in video clips posted on the Twitter account of his son, Panthongtae, on Friday.
Thaksin's family, friends and supporters threw him a party in London on Thursday, which he described as one of the happiest nights in his life.
With an election planned for next year, Thaksin said Pheu Thai would return to power.
"We know what they want. We know what they're looking for," he said, referring to his compatriots in Thailand.
"They are looking for a party with solutions. I believe the Pheu Thai Party is the solution to Thailand," he added.
Pheu Thai will see a "landslide" victory in the next poll, Thaksin said.
The parties he founded and supported -- from Thai Rak Thai to Pheu Thai -- have won every election since 2001, despite two coups and numerous lawsuits against him, as well as his family and party members.
But Pheu Thai and its alliance, the United Front for Democracy against Dictatorship, are facing challenges by the Sam Mitr (Three Allies) group. The political group, dominated by his former supporters Jungrungreangkij, former industry minister Somsak Thepsuthin, are trying to lure the party's former MPs to its side. Mr Somsak said on Thursday the group supported Gen Prayut to continue his premiership.
Thaksin's sister Yaopawa and some Pheu Thai members were in London for his birthday party, joining his other sister Yingluck, who fled a jail sentence in Thailand last year and was living with him there.