In many countries, this is a complex question, but in Australia, the answer is simple: by and large, gamblers never have to pay taxes on their winnings. As gambling isn’t considered a profession for the vast majority of players, it isn’t taxed as such; rather than income, the government sees gambling winnings as a fortunate windfall, and allows players to keep the entirety of their winnings.
It’s unlikely, as even professional poker players – certainly the gamblers whose winnings would be most likely to have been based on skill – haven’t been asked by government to pay taxes on their winnings. If, for some reason, such a player were to set themselves up as a business, then they might be required to pay taxes, but it’s an unlikely scenario. On the other hand, any sponsorships, endorsements, or other gains earned because of their poker career would of course be taxable.
Since we’ve said that Australian gamblers don’t pay taxes on their winnings, it’s reasonable to ask how state governments collect so much tax revenue from gambling! Since close to 10% of state revenue comes from gambling, clearly someone is paying a lot of money to the tax man.
The answer is that gambling operators shoulder the burden of taxation rather than players. Depending on the state and the type of gambling involved, the rate of taxation and how it is calculated can vary. Casinos and venues with pokies pay licensing fees for the right to have those machines in the building, and operators also pay taxes on their profits, either based on player losses or net profits.