Lambert will be the headline act of a lavish New Year's Eve show organised and televised live nationally by state-owned broadcaster MediaCorp.
Over the course of the week, thousands of Singaporeans have flocked online to sign two duelling petitions.
One, started on Wednesday, calls on MediaCorp and the government to drop Lambert, on account of his support for gay rights and reputation for risque performances, which it called "contrary to mainstream Singaporean values".
Comments on the petition called Lambert's performances "disgusting", "disturbing" and "lewd". "Please give more wholesome role models to our youths," said one petitioner Elaine Lui.
A counter petition was started on Thursday night and quickly gathered steam, calling on organisers to keep Lambert as a demonstration that Singapore "shuns discrimination and promotes diverse inclusive points of view".
"In no way whatsoever does his sexual orientation have any relation to his role as an entertainer and singer. Asking for him to be banned on TV is ludicrous and is akin to asking retailers to stop selling iPhones because [Apple has a] gay CEO," said commenter Ivan Lin.
As of Friday evening, both petitions were neck-to-neck with thousands of signatures each, drawing in supporters from Malaysia, Australia, Hong Kong and Japan as well.
Lambert previously performed in Singapore in 2013 to few complaints, and concerts by other artists such as Lady Gaga have generated greater controversy.
The debate over Lambert this time stems from a cultural divide in Singapore that has widened recently.
A modern and open city-state with a thriving gay scene and liberal minority, much of its society also remains deeply conservative. A religious right, supported by some Christians and Muslims, has grown in tandem with a burgeoning gay rights movement.
The annual gay rights event Pink Dot, where supporters don pink as a message of inclusion, has sparked a counter campaign called Wear White where conservatives tog themselves in white as a symbol of purity.
Both sides have become more vocal in recent years, and though the conflict has not gone beyond heated debate, it has unnerved Singapore officials charged with maintaining the peace on the tiny island.
They have tried to strike a balance. A controversial law that bans gay sex - a key flashpoint in the divide - remains on the books, but the government has promised never to enforce it.
Authorities have also sought to rein in both camps by curbing their public demonstrations, in some cases refusing permits to both conservative and gay rights groups to hold or expand their public events.
As for Lambert, they appear to have come to a compromise.
MediaCorp has not dropped him - but has promised that the show will conform to strict broadcast regulations and be made "suitable for family audiences".
Meanwhile, Lambert has said in a statement that his performance would "celebrate the entire human family in all its diversity" and that he was "a uniter, not a divider".

National Grid applied to install the overhead line which would carry electricity from the proposed new nuclear power station, Hinkley C.
The Planning Inspectorate has announced it will hold a six-month inquiry, during which local people can comment.
It will then make a recommendation to the Secretary of State.
Sir Michael Pitt, chief executive for the Planning Inspectorate, said the application "met the required tests" and the decision was made after "careful consideration".
"The applicant must now decide when to publicise the fact that its application has been accepted to proceed to examination and announce when members of the public will be able to register with the Planning Inspectorate as an interested party in the application," he added.
The National Grid plans were submitted last month. A company spokesman previously said it had taken "five years of consultation".
It will see 30-miles of overhead wires carried on pylons and a five-mile section under the Mendips, connecting the station, near Bridgwater, Somerset, to the National Grid's 400,000 volt substation at Avonmouth.
It would also see the removal of 246 pylons and 42 miles of cabling between Bridgwater and Avonmouth, and Nailsea.
Those against the pylons argue the entire route should be underground or sub-sea - but National Grid had previously said this option would be too expensive.
Now the plans have been accepted for examination, the documents will become public. A final decision will not be made until late 2015.
A growing controversy over a Singapore concert starring openly gay US singer Adam Lambert has highlighted a widening cultural divide in the strait-laced city-state.
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Plans for more than 140 pylons connecting Hinkley Point to Avonmouth have been accepted for examination by the government.