Sri Lanka's top court found President Ranil Wickremesinghe guilty of "unlawful conduct" on Thursday for delaying by more than a year local polls seen as an unofficial referendum on his handling of the economy.

Since Wickremesinghe enjoys immunity while in office, the judgement carries no immediate legal consequences, but the state of the economy is expected to be a key issue for voters in presidential elections next month.

Because the local polls were postponed, the 21 September election will now be the first vote since Wickremesinghe took over two years ago after protesters furious at an unprecedented financial crisis toppled strongman president Gotabaya Rajapaksa.

Wickremesinghe, 75, is seeking re-election for a five-year term next month, and faces a daunting challenge from rival candidates.

A five-judge bench of the Supreme Court on Thursday unanimously held that Wickremesinghe failed to release money to conduct the local government elections in March 2023.

Wickremesinghe's administration said the money in state coffers was needed to pay public servants and pensions, despite a previous court order to finance the vote.

The court said Wickremesinghe's "arbitrary and unlawful conduct" in preventing the local polls had resulted in the infringement of constitutional rights.

The court ordered the independent election commission to hold the local polls as soon as possible, but without disrupting the upcoming presidential vote.

The state was also ordered to pay the legal fees of four petitioners who challenged the indefinite postponement of the polls.

Wickremesinghe, previously an opposition member of parliament, was elected by lawmakers in July 2022 as interim president after his predecessor Rajapaksa quit due to the protests over the economic crisis.

Wickremesinghe secured a $2.9 billion bailout loan from the International Monetary Fund (IMF) in March 2023 after doubling income taxes, removing energy subsidies and increasing prices.

The local poll scheduled for March 2023 had been widely seen as a referendum on the unpopular austerity measures taken to secure the IMF bailout.

Opposition lawmakers accused Wickremesinghe at the time of using the economic crisis as an excuse to sabotage democracy.