What is the process for obtaining a Tax Identification number and submitting a tax return in Thailand for those staying over 180 days?

You only have to file a tax return if you actually have a tax liability in Thailand. If you bring untaxed money onshore then you have to file a tax return but if the money is taxed in another country that has a double taxation treaty then you do not have any liability here. There has been lots of talk about the 'new' tax rules but there are none this has always been the case. The same with the 180-day rule. There was an amendment to the existing rules which came into force on Jan 1st. It said any untaxed money brought onshore will be liable for tax. Previously if the untaxed money that was brought to Thailand was earned in a previous tax year then it was deemed tax-free. This loophole has now been closed and all untaxed money is now liable for taxation.

This is the guidance from the official source .html