Rainsy, leader of the Supreme-Court dissolved Cambodia National Rescue Party (CNRP), arrived here from Malaysia where he met parliamentar on Tuesday, reports Efe news.
He thanked the Indonesian government, which he said "has invited me to be in Jakarta for a few days", and added that the country was an example of a "real democracy".
"In a democracy, the opposition can become the ruling party, the ruling party can become the opposition... It changes from time to time. But in Cambodia we have the same ruling party for 40 years, and we have the same prime minister for 35 years," he said, referring to strongman Hun Sen, who has ruled the country since 1985.
"Why is he afraid of me? I have bare hands, I have no weapons, I have no army, I have no money so why are they so afraid of me?" he asked of the Cambodian government who have gone to great lengths to prevent his return, including reinforcing entry points with the military.
Rainsy, 70, was scheduled to arrive in Jakarta on Wednesday night but said on social media he had missed his flight. Amid reports he had been denied boarding in Malaysia at the request of Indonesian authorities, he reiterated to reporters Thursday that he "just missed his flight".
His arrival in Indonesia comes after he made headlines when he said that he was refused permission to board a flight from Paris to Bangkok, from where he was to enter Cambodia.
The opposition leader, who holds a French passport, instead flew to Malaysia where he was invited to the parliamentary meeting.
Rainsy fled Cambodia in 2015 to avoid being imprisoned for defamation and other charges he considers political fabrications.
The government of Hun Sen, the world's longest-ruling Prime Minister, has called the exiled opposition leader and other CNRP members' intentions to return a "coup attempt", although his deputy said Rainsy was not barred from entering the country.
Hun Sen on Thursday announced that more than 70 people rounded up in the lead up to Rainsy's scheduled return would be released on bail.
( With inputs from IANS )