Former Thai Prime Minister Thaksin Shinawatra is flying home from Hong Kong after 17 months away.
Supporters are waiting for Thaksin in Bangkok
He said he would defend himself against unfair accusations and said he had faith in the Thai justice system.
Mr Thaksin faces allegations of corruption in Thailand, brought by the leaders of the September 2006 coup which removed him from office.
Large crowds of his supporters are waiting at Bangkok airport to welcome him back to the country.
He still has strong popular support in Thailand and analysts fear his return could prompt further political unrest.
"Nobody can push him out. He is a good guy. Thai people love him," said one supporter, quoted by the AFP news agency.
Mr Thaksin told reporters that he was confident of his innocence and was ready to prove he had done nothing wrong.
He said he would report to the authorities on his arrival.
Current Prime Minister Samak Sundaravej said he welcomed his former ally's return.
"It's normal that he must defend himself in the court and my government will not interfere," Mr Samak said.
Mr Thaksin's party, Thai Rak Thai, was outlawed following the coup and he was personally banned from politics for five years.
Thaksin Shinawatra was ousted in September 2006
But many of his followers went on the form the People Power Party (PPP), which won elections in December last year.
Mr Thaksin has insisted that he does not plan to get involved in politics on his return, but the BBC's Jonathan Head in Bangkok says that as the PPP's main financier, Mr Thaksin has great authority.
Mr Thaksin said: "I just want to be going back as a normal citizen and would like to live my life peacefully with my family.
"Democracy returned to Thailand. So, it is time for those who are democratic advocates to go back."
Our correspondent says Mr Thaksin's millions of supporters will see his return as final proof that the coup leaders failed to destroy his political career.
There is expected to be heavy security surrounding Mr Thaksin's arrival.
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