The Pakatan Harapan, a four-party alliance driven by Tun Dr Mahathir Mohamad and Mr Anwar won the general election last week, ousting the ruling Barisan Nasional coalition for the first time in the history of the Southeast Asian nation.
Mahathir will stay in power until the administration's mid-term before handing over power to Anwar.
Anwar began serving a five-year jail sentence in February 2015 after the Federal Court upheld his conviction and sentence on a charge of having sodomised a former personal aide.
Malaysia jailed opposition icon Anwar Ibrahim waves to supporters as he leaves a hospital in Kuala Lumpur, Malaysia, Wednesday, May 16, 2018.
Anwar, who was the deputy prime minister during Mahathir's premiership in the 1990s, is now in a hospital in Cheras, waiting for the Pardons Board meeting, scheduled for Wednesday morning, said Bernama. He will meet with the king at the national palace and then speak to supporters at a rally on Wednesday evening.
Anwar is seeking a royal pardon on the grounds of "miscarriage of justice", which would reverse his conviction and make him eligible to actively participate in politics.
It was a shared desire to remove scandal-ridden former-PM Najib Razak that forged the unlikely alliance between Anwar and Dr Mahathir, who came out of retirement to bring down his former protege.
"My children were quite young during the earlier period of incarceration [from 1999 to 2003] and that was a hard period for them and [his wife, new deputy prime minister Wan] Azizah", he said. It was the second time he had been convicted of the sodomy offense.
He was found guilty of corruption in 1999 andgiven a five years jail, and the following year was also found guilty of sodomy.
Mahathir has said he expects to run the government for up to two years but has signalled the reins would be turned over to the Anwar eventually.
Anwar said that after working with Mahathir for many years, "I understand that he cares deeply about Malaysia and the people of Malaysia. a new partnership was essential to overcome the deeply entrenched, corrupt system that was presiding over Malaysia". But Anwar needs to win a by-election to become a parliamentary member first.