At Iswaran’s sentencing last October, the court heard that Iswaran requested Ong bill him for a business class flight to Doha, after he discovered that he was being investigated.
The judge said that he acted with deliberation and premeditation to avoid the probe.
On Monday, Ong pleaded guilty on Monday for helping Iswaran pay the Singapore Grand Prix for the flight ticket from Doha to Singapore.
The judge said that Ong’s sentencing would be held on 15 August.
Ong faces up to two years in jail for abetting a public servant in obtaining gifts, while the maximum jail term he faces for the abetment of obstruction of justice is seven years.
The 79-year-old is also accused of abetting Iswaran in obtaining an all-expenses paid trip to Doha, said to be worth around S$20,850 ($16,188; £12,194).
The two men were arrested in July 2023 and charge sheets revealed that Iswaran was gifted more than S$403,000 ($311,882; £234,586) worth of flights, hotel stays, musicals and grand prix tickets.