Can I change my Non-B visa with work permit to Non-O visa (marriage) without leaving Thailand?

@Brandon ***********

is correct.

Keep in mind that your nonb extension finishes the DAY you stop working.

If the WP expires or gets canceled your are overstay from that date.

Once your reason for extension ends, it's done.

If you are not prepared to apply for the marriage extension immediately you may be able apply for a 1 time 60 day visit Thai family extension.

To give you time to sort out the rest, usually the money.

First, check with your immigration office to see what they will allow you to switch reasons for your extension.

If they are okay with it, the only way to do it is like this:

1) You must be on a work extension, not an original 90 day non-B VISA.

2) When your extension is coming up for the next annual extension, you do not apply for the extension based on work, instead you submit your application for an extension based on marriage.

You may also possibly be able to switch if you are going to stop working. You would still need to check with your immigration office on this as well. What you would do is get a letter from your work stating your last day of work and take it to the labor department to cancel your work permit. Then you take that same letter along with your cancelled work permit to immigration and cancel your work extension. At the same time you apply for an extension based on marriage. Some immigration offices might allow this and some might not, that's why you need to go there and check first.