There is actually no such thing as a 'marriage visa' in Thailand. Foreign nationals who are married to Thai citizens are entitled to apply for an 'O' Class Dependent's Visa. Applicants must be able to prove that they have either B400,000 deposited in a Thai bank account, or have a guaranteed monthly income of B40,000, or a combination of the two, so that your total income is equal to or greater than B400,000 per annum.