The country you reside in is generally the country you have to pay tax in. The ATO considers you an Australian resident for tax purposes if you meet any of the following conditions:
you are born and bred in Australia;

• you are living permanently in Australia;
• you have been living in Australia for at least six months and have worked most of that time at the same job and lived at the same place; or
• you have been living in Australia for more than half the financial year, except where your usual home is overseas and you do not intend to live in Australia permanently.

As you are an Australian resident, you are taxed on your worldwide income. As a result, any foreign income must be included in your Australian tax return as assessable income.

Whilst the US taxman would obviously want a piece of the tax pie, there is an agreement between the Australian and US governments to avoid double taxation of income. US tax is restricted to only dividends (15%) or interest (10%) that you might derive from the United States in your trading activities. You are entitled in your Australian tax return to a foreign income tax offset for the amount of any US tax paid. The only way the United States could tax your trading income is if you operated through a permanent establishment, but there is a specific exemption if you are merely using US brokers.

Don’t try to hide the income from the taxman. The ATO has tax treaties with 46 countries, including the United States, which allow it to exchange information about offshore income and transactions. Any data received is matched against Australian tax returns. The ATO also receives information from AUSTRAC, which monitors domestic and international transactions of more than $10,000.