Ex-transport minister S. Iswaran, known for helping bring Formula One to the financial hub, was earlier this year hit with 35 charges mostly related to graft in a nation often cited as one of the world's least corrupt.

But prosecutors moved forward with five lesser charges only, including some related to a billionaire property tycoon.

"S. Iswaran pleaded guilty to and was convicted... of four charges for obtaining gifts from two local businessmen. He also pleaded guilty to and was convicted of one charge for obstruction of justice," the attorney general's office said in a statement.

Prosecutors are seeking six to seven months in prison combined for the charges, while the defence is hoping for no more than eight weeks, The Straits Times reported. 

The sentencing date has not been formally announced by the attorney general's office, but local media said it was set for October 3.

After the court session ended, 62-year-old Iswaran said he could not comment on the trial.

"I just want to thank all of you for coming, and let's see how it goes," he told reporters outside the Supreme Court.

His trial has been deemed by observers to be one of the most politically significant in the city-state's history.

It also risks damaging the reputation of the ruling People's Action Party (PAP) before general elections expected to be held by November next year. 

Iswaran quit in January after being formally notified of the charges which include accepting gifts worth more than $300,000. 

In a resignation letter at the time, he said he would clear his name in court.

Iswaran has paid back around $295,000 in financial gain to the government and gifts including a Brompton bicycle were also seized from him, the attorney general's office said.

The charges include obstruction of justice relating to an attempt to block Singaporean authorities from investigating a business class flight at the expense of Malaysian hotel tycoon Ong Beng Seng, one of Singapore's richest residents.

The other four charges relate to his receipt of gifts from Ong, the managing director of Hotel Properties Limited, and a top director at a construction company, including bottles of whiskey and golf clubs.

Neither businessman has faced punishment.

The charge of obstructing justice carries a maximum sentence of seven years and a fine, while accepting gifts of value has a maximum sentence of two years and a fine.

Salary payback 

Most of the charges against Iswaran have been levelled with a rarely used criminal law that states it is an offence for public servants to accept objects of value from figures they officially work with.

Singapore's former prime minister Lee Hsien Loong said at the time of Iswaran's resignation that he had pledged to return money received as part of his salary and allowances since his arrest.

Cabinet ministers are paid salaries comparable to the top earners in the private sector to deter corruption.

Lee has previously admitted that his long-ruling PAP had "taken a hit" after a spate of political scandals.

Last year two PAP legislators resigned for having an affair.

Before that, two heavyweight cabinet members were investigated for allegedly getting favours in their rental of sprawling colonial-era bungalows, but were subsequently cleared.

Prime Minister Lawrence Wong, who succeeded Lee, has said the PAP's anti-corruption stance is "non-negotiable".

The government said it would review the terms of its Formula One Grand Prix deal after Iswaran's resignation. This year's race in Singapore concluded on Sunday.

Singapore's last senior politician convicted for graft dates to 1975, when Wee Toon Boon, then minister of state for environment, was found guilty of accepting bribes worth more than $600,000 according to local media.