He pretended to be a professor in child psychology and lied to the authorities about his HIV status to get jobs at local polytechnics.
He even used his lover's blood for an HIV test so that it would test negative for the condition.
Over about eight years, American citizen Mikhy K. Farrera-Brochez, 32, committed offences including cheating, lying to a public servant, possessing drugs and using forged educational certificates.
Yesterday, he was sentenced to 28 months' jail.
He pleaded guilty to six charges, with 17 taken into consideration.
Three other charges, which had been taken into consideration, were later stood down to be mentioned at a later date.
In 2008, Farrera-Brochez moved to Singapore, a year after he began a romantic relationship with a local doctor, general practitioner Ler Teck Siang, 35.
To apply for an Employment Pass (EP) to stay in the country with his lover, he submitted an HIV negative blood test result to the Ministry of Manpower (MOM) in March that year.
However, Farrera-Brochez, who is HIV positive, had used Dr Ler's blood for the test by visiting a clinic in Commonwealth where Ler was on duty.
Ler had drawn the blood from his arm that day and labelled the test tube holding his blood with Farrera-Brochez's particulars.
MOM then issued Farrera-Brochez with an EP, and he later worked as polytechnic lecturer teaching psychology and early childhood education.
He similarly duped the authorities in 2013 when he tried to apply for a Personalised Employment Pass (PEP), which would let him change employers without applying for a new EP.
He was also found guilty of possession and consumption of ketamine and amphetamine in May last year.
Investigations further revealed his educational certificates, including a doctorate degree in psychology and education from the University of Paris, were forged.
Deputy Public Prosecutor Suhas Malhotra said he had conspired with Ler to falsify the test results.
"His conduct evinces a blatant disregard for the authority of our laws," he said
Ler, who is also facing charges, has not been dealt with.
This article was first published on March 2, 2017.
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