According to the Herald Sun, the man told Magistrate Grant Riethmuller he shouldn't have to pay for the inadvertent offspring given the circumstances of the conception.
He said that he'd had "a consumer transaction" with the child's mother, reports News.com.au.
The accidental dad said it was implied in the "contract" that the woman should have been taking measures for birth control.
The prostitute, known only by the pseudonym Ms Logan, did not appear in court, and details of her employer were not publicly revealed.
The magistrate heard the man had been paying casual child support payments of 100 dollars each week before he lost his 140,000-dollar-a-year job.
He allegedly cut the payments when he took another job with a significantly reduced salary and ran into money troubles.
Riethmuller also heard the man had a child with his ill wife.
However, the magistrate this week ruled the circumstances of conception had no bearing over the case and ordered the man to continue the 100-dollars a-week payments.
Sex without a condom is illegal in licensed Victorian brothels and escort agencies.