Anwar, 70, left a Kuala Lumpur hospital at 11.30am local time, after receiving a long-awaited royal pardon just an hour earlier.

In chaotic scenes, he waved at supporters and hundreds of journalists before being bundled into a car by police officers, who then hung onto the vehicle.

Later, speaking for the first time since his release, Anwar pledged his full support to the new government as a "concerned citizen".

He said the historic election win by Malaysia's opposition last week had sent a message to the entire Muslim world that democratic change is possible.

"My determination is to help the people of Malaysia ... my struggle has been going for 20 years," he said.

"Today is a new beginning.

"I fully support Mahathir and Wan Azizah's leadership, as an ordinary citizen I support them all the way."

Anwar said he would not "demand or insist" on an immediate time frame for the hand over of the prime ministership from Mahathir to himself - as long as reforms to the judiciary, media and the "entire apparatus" got under way.

Before the election Anwar and Mahathir - former foes and political allies - had reunited in an ultimately successful attempt to blast Najib Razak out of the top job. Under that deal, the 92-year-old Mahathir agreed to hand power to Anwar at a point in the future.

The election win, which ended 61 years of one party rule, had marked the started of a new dawn for his country - now it was up to the newly-minted Pakatan Harapan government to honour its commitment to reform.

"I must thank the people of Malaysia ... the entire spectrum of Malaysians, regardless of race and religion, who stood by the principles of democracy and freedom. They demanded change," Anwar said.

The Muslim world, he said, could now see there is a "window of opportunity, if given a chance, even minimum chance, for democratic change".

Anwar was at pains to stress that Malaysian King Muhammad V of Kelantan had granted him an unconditional pardon - he had been jailed on a questionable sodomy charge by Najib's regime.

"We appealed because there was a miscarriage of justice, we appealed because there was travesty of justice. We appealed because there was clear conspiracy to condemn me, assassinate my political character."

"Praise to Allah because the king accepted this, the pardon is complete, unconditional."

He also called for Najib to be brought to book over allegations of corruption but he bore no personal animosity, he said.

Anwar was convicted of sodomy in 2015 in a case he has said was aimed at crushing his alliance after making gains against the government.

He planned to address party supporters at what is expected to be a huge rally outside the party's headquarters at 10pm on Wednesday.

It's expected he will be prime minister within two years.

Inside and outside of Malaysia there's eager anticipation for his comeback.

Foreign Minister Julie Bishop told AAP the Australian government had followed Anwar's trial closely and was pleased he could now participate fully in politics.

"Anwar has much to contribute to Malaysia," she said.

In an exclusive interview with Fairfax Media on Tuesday, Anwar said his country was on the verge of a new "golden era", adding, "I never lost hope" during his years in prison.

The man who has led the country's reform, or "reformasi" movement for 20 years, cautioned his countrymen and women, saying "one election does not a democracy make".

Anwar has spent eight of the past 20 years in prison on politically-motivated sodomy charges, and as his one-time rival, Mahathir Mohamad, secured a remarkable election victory six days ago, he was in hospital recovering from shoulder surgery.

But, he said, he had never lost hope.

"I always believed in the wisdom of the people and that if we fought hard enough we would eventually prevail," he told Fairfax Media.