What steps should I follow to get married in Thailand and obtain a British passport for my baby?

Get her here on a tourist visa. Baby born British 😁

Do yourself a favor and get a paternity test after the birth.

Being born in Australia hasn't made you Australian since 1986

In order to get married legally, and not just a ceremony with monks, you will need a right to marry document notarized by your embassy. This has three choices, never married, divorced, or widowed. Divorced and widowed require supporting documents, your divorce decree, or in the case of widow, the death certificate. Never married requires nothing else. After you get this it must be translated into Thai, and then verified that it is an accurate translation and stamped by the ministry of foreign affairs. You must have this in order to get legally married at the local Amphur. Once you are married you can get a long term type O visa extension based on Thai wife, and that you have a Thai bank account in your name only, and that you put at least bt400,000 (it can come from anywhere) in it at least two months before you apply for this type O visa extension, plus other documents that are pretty easy to obtain. Then you can get a one year extension, and keep extending it every year with the same updated documents.

Good luck on that

Don’t forget about dowry 🙂

Plenty of good advice mentioned. Don’t worry, it’s fairly straight forward.

Mark Jacobs is good for sorting you a passport out if you are unable to get to Bangkok to do it yourself, I got referred him by someone else, haven't actually done it yet but I hear he offers a good service

As

@Peter ********

says, first make sure your name is shown on the Thai birth certificate and get it translated into English. You apply for the baby's UK passport via HMPO at VFS in Bangkok or Chiang Mai. Fill in the application form and check what supporting evidence is required. You will need your original long-form birth certificate to show you are British Otherwise Than By Descent and the baby's photos will need to be countersigned by a upstanding Brit who knows you! You can use an agency if necessary. I can recommend one but many others will too. It's fairly straightforward to do it yourself, if it's easy for you to get to VFS.

Follow this link.

You will need birth certificate showing you as father 1st