Government leaders scorned the candidacy of Mahathir, who will be the world's oldest leader if the opposition wins. Government minister Abdul Rahman Dahlan called his candidacy a stumbling block to the opposition's reform agenda.
"It's laughable for (the opposition) to appoint Mahathir as the next PM and expect him to implement those reforms," he tweeted. "It's a tragedy to their own cause ... anyway, I thank (the opposition) for making it even easier for (the ruling coalition) to win the upcoming general election."
Mahathir, Asia's longest-serving leader for 22 years before stepping down in 2003, was an authoritarian who made a high-profile return to politics in a bid to oust his protege Najib.
Najib has sacked critics in his own government including an attorney general and deputy prime minister and muzzled the media since the scandal erupted two years ago. The US and several other countries are investigating allegations of cross-border embezzlement and money laundering at 1MDB, a state investment fund set up and previously led by Najib to promote economic development but which accumulated billions in debt.
Najib has denied any wrongdoing.The opposition coalition Sunday also agreed on allocation of seats for the polls and to limit the prime minister's tenure to two terms if they win. The coalition, which includes the party led by jailed former deputy Prime Minister Anwar Ibrahim, also said they will seek a royal pardon for him so that Anwar can take over from Mahathir as the next prime minister.
Anwar was Mahathir's deputy until he was sacked in a power struggle in 1998 and later imprisoned on charges of corruption and sodomy that Anwar said were trumped up.
Anwar was freed in 2004 but in 2015 he returned to prison following a second sodomy conviction that critics said was a political conspiracy to break up the opposition. He is due for release in June.
Mahathir told The Associated Press in an interview last year that the opposition could win a simple majority in the polls by tapping into anger at Najib's corruption scandal and rising cost of living.
- AP