The tradesman was using a portable toilet on a Sydney building site on Wednesday morning when he was bitten.
A spokesperson for St George Hospital confirmed that a 21-year-old man was treated for a redback bite.
The redback spider, closely related to the black widow spider, is distinguished by a long red stripe on its abdomen.
The spider's bite causes severe pain, sweating and nausea.
The BBC spoke to the owners of the property who confirmed that the man had been bitten on the penis as described in media reports.
He was later discharged from hospital in a stable condition.
Although there are recorded cases of deaths from redback bites, none have occurred since the development of antivenom in 1956.
An Australian man has taken himself to hospital after a venomous redback spider bit him on the penis.