Malaysia's Anwar Ibrahim will face the first test of his return to political life on Saturday, in a by-election that would pave his way to claiming the premiership, as promised by former foe Prime Minister Mahathir Mohamad.

Anwar, who is expected to win, needs a strong mandate in the fight in the coastal seat of Port Dickson to counter criticism that he is in a hurry to take over from the 93-year-old Mahathir, just five months after being released from prison.

"A bigger margin will give the by-election the appearance of a coronation, something Anwar has been awaiting for 20 years," said Adib Zalkapli, an analyst with the political risk consulting firm Vriens & Partners. "If he wins by a smaller margin, he may be seen as merely riding on the popularity of Mahathir, without winning new support to the coalition."