In a series of Facebook comments, Sonny Truyen suggested Singapore was an undesirable place to live due to the unavailability of the smartphone game.
He also wrote that Singapore was filled with "stupid people".
Several Singaporean web users contacted his employer, real estate website 99.co, expressing anger at his posts.
During a dispute with another Facebook user, Mr Truyen wrote that "the average IQ" in Singapore would fall if he left the country, and that "locals can't even read".
Darius Cheng, chief executive of 99.co, apologised for Mr Truyen's comments in a blog post, and said his employment contract had been terminated.
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"Sonny, as an SEO specialist, has only started consulting for us for a week before the incident happened," Mr Cheng wrote.
"We are a proud Singaporean company and do not condone such language or behaviour, hence we have since terminated his engagement once the incident came to light."
Responding to the online anger at Mr Truyen, Mr Cheng also asked readers not to spread "messages of hate and division, but instead embrace our diversity".
"Anyone labelled a 'Foreign Talent' was heavily criticised" online after the incident, he said. "I am sure we all have Australian or Vietnamese friends - how would they feel if they read it?"
Large numbers of Western expats live in Singapore and Mr Truyen is not the first foreigner to be fired amid a social media furore.
In 2014, British banker Anton Casey posted a YouTube video complaining about the "stench" of Singapore's public transport system, which he said was full of "poor people".
Mr Casey lost his job and was forced to flee the island nation.
Australian executive Amy Cheong was also sacked and fled Singapore in 2012 after posting racist comments on Facebook after she was kept awake by a wedding being held near her home.
Authorities in Singapore are known to take strong action against public comments that are considered to breach standards of decency.
Mr Truyen told Mashable: "It was disappointing the lengths Singaporeans went at to attack me and deny [me] any chance of making amends for my actions."
He has deleted his social media accounts, saying it was a "very big error in judgement to negatively label an entire country over Pokemon".
An Australian has been sacked after a profanity-laden rant on Facebook, where he complained that the game Pokemon Go is not available in Singapore.