Nigel Skea, 52, from Southampton was also fined 1,000 Singapore dollars (£539), while his then-fiancee, Agatha Maghesh Eyamalai, was given a week’s prison sentence. The couple are now married.
People in Singapore are required to spend two weeks quarantining in a hotel upon arrival.
Court documents showed Skea left his room at the five-star Ritz Carlton Millenia hotel in Singapore on three occasions in September to visit Eyamalai.
On Monday, Skea pleaded guilty to one charge of contravening a control order and one of failing to wear a face mask.
Eyamalai admitted one charge of conspiring to contravene a control order.
The court heard how on one occasion Skea left his hotel room and climbed 13 flights of stairs to spend nine hours with Eyamalai, who opened an emergency exit door for him.
District judge, Jasvender Kaur, said the sentences were meant to send a “clear message” about the importance of following lockdown restrictions.
Skea is the first Briton to be jailed in Singapore for breaking coronavirus restrictions.
It comes after a quarantine hotel worker and woman quarantining in New Zealand were caught in an “inappropriate encounter” where physical distancing was not taking place.
The woman, who was supposed to be avoiding all physical contact with others for 14 days at the Grand Millennium Auckland hotel, was served with a formal written warning by the police for breaching the mandatory quarantine.