Nigel Skea, 52, walked up an emergency staircase to spend the night with Agatha Maghesh Eyamalai, 39, in September. The couple are now married.
Eyamalai admitted aiding him. Breaking the rules could bring six months in jail, but the prosecutor has sought a lesser period and fines.
Singapore requires people to spend 14 days in a hotel upon arrival.
In a district court on Monday, Skea pleaded guilty to one charge of contravening a control order and one of failing to wear a face mask.