On Tuesday, Mahathir said he expected to be prime minister for one or two more years, setting off talk of differences between the two.
"In fact, even from within the prison cell I sensed that the outrage against a corrupt regime was increasing by the day".
PKR communications director Fahmi Fadzil said earlier that Anwar is scheduled to hold a press conference at his home in Segambut at around 4pm.
In 2015, Anwar was imprisoned for a second time, again on sodomy charges that he said were false.
His bruising fall was widely seen as politically motivated.
"The pardon timing is fast, and this speaks to the recognition that his conviction was unjust", said Bridget Welsh, a political science professor at the John Cabot University in Rome.
Mr Mahathir has promised to step aside for Mr Anwar to become prime minister within two years.
But it has not been all smooth sailing since the historic win, with concerns over the slow formation of the cabinet as different parties in the winning alliance jostle for positions.
Yesterday, Dr Mahathir met Auditor-General Madinah Mohamad, who announced the declassification of the report and said its executive summary would be available on her department's website. He added that he would make the final decision about cabinet posts.
Mr Anwar sought to allay those concerns, saying he was not in a hurry to take over from Mr Mahathir.
Anwar's People's Justice Party (PKR), which has the most seats in the alliance, is demanding a proportionate number of posts in the cabinet.
In the 1990s, Anwar served as deputy prime minister under Mahathir. Mahathir sacked and jailed Anwar on charges of sodomy and corruption.
An advocate for reform, clean government and an end to the previous government's authoritarian ways, Anwar made no immediate comment but was expected to address the public in the afternoon followed by a political rally in the evening.
Anwar and Mahathir agreed in 2016 to join forces with the aim of ousting scandal-hit Najib Razak and his Barisan Nasional (BN) alliance.
In the WSJ report published online Tuesday, Dr Mahathir reportedly said he would not offer Najib freedom in an effort to reclaim the missing funds.
"Going to jail I consider a sacrifice that I make for the people of this country", he said at the time.
A person described in the United States lawsuits as "Malaysian Official 1" was said to have received more than US$1 billion in 1MDB funds, some of which was used to buy jewellery for the person's wife.
The US Department of Justice has said that more than $4.5bn was misappropriated from the fund. nearly $700 million appeared in Mr Najib's bank accounts before the 2013 election.
He said that Anwar, a former enemy turned ally, may be just a member of parliament for a while.
Reuters reported that the Malaysian Anti-Corruption Commission found evidence in late 2015 that RM42mil was transferred from a former subsidiary of state fund into an account of Razak.
Najib denies any wrongdoing in connection with losses at the fund. Mr Najib and his wife were barred on Saturday from leaving the country as a leaked flight plan revealed they were planning to leave for Indonesia.