How long before leaving Australia should I apply for my 90-day Non-O visa for Thailand?

Have you done your No impediment to marry form from the Aussie embassy in Bangkok, then filed at Thai Consulate that taks 30 days to come back. Then you go to the Amphor with all your forms and register you Marriage, you have to make sure your partner has all there paperwork just like you have all this can be done on tourist visa once you have all that done then you apply for your none o visa then once you have that then you can open bank account 0 bhat into term deposit and that stays in the bank then you go to immigration and sort out your marriage visa. Remember to marry in Thailand it's the Amphor signature that is important not the ceremony. Also it is best to use an agent and you will find them just up the road from the embassy.

Make sure your partner is marrying you for love not your money Good luck,

The non-O IS the marriage visa. What you'll be applying for in Thailand is an extension, not a visa since you'll already have one.

A non-O visa is valid for 90 days. So realistically you can apply any time in the 3 months before you plan to go to Thailand. But a month should be plenty of time.