I have an extension of stay based on marriage and my work permit was obtained through this. My extension of stay is current till March 2015. I will be leaving my job effective 15th September 2014.

Do I have to go to Labour myself and cancel or does the company do it?

Any help regarding actual what is the procedure to cancel my WP would be appreciated.

Either you or the company can do it. There is even a form for it, to be downloaded from immigration website.

If you do it yourself, visit the labour office with your WP and a letter from the company clearly identifying your last day of employment.

Here's the WP cancellation from with instructions for either you or your employer to cancel.

wp_cancellation.pdf

...and you only have 24 hours to do that and leave the country. TIT

...and you only have 24 hours to do that and leave the country. TIT

Read again. The OP is not in Thailand based on his job but based on his marriage.

OP - you asked: "Do I have to go to Labour myself and cancel or does the company do it?"

No you don't have to cancel it. You can cancel it if you want to, but you do not have to.

Your employer might decide to cancel it if you give him power of attorney in this matter. (The form to which another poster gave a link sites that this will be needed if your employer decided to cancel it).

Once your WP is cancelled you will have to cancel your extension of stay at the immigration the very same day. To do that, bring the company letter that indicates your last day of employment, the labor office cancellation slip and your Phor Ngor Dor 91 tax document.

This is the procedure for a non-immigrant B visa, not sure it's necessary in your case.

You do not have to cancel your work permit or at least nothing will happen if you dont. However, it does make things easier if you require another one later. Check with your employer, sometimes they do this for you. What ever the case it is not hard to do fill out the form hand it in and get a letter of receipt.

As your permit was based on marriage you will not have to leave the country.

I did read, (maybe here) that a new rule is being considered or introduced where you will no longer need to leave the country if you are changing jobs. I am also not sure if this applies specifically to teachers or all employment streams.

...and you only have 24 hours to do that and leave the country. TIT

But the OP is on an extension based on marriage. So there is no impact on his visa status and no need to leave the country. That is one of the advantages of working on a marriage extension. The drawback is more hassle getting the extension and having to take the missus along.

You do not have to cancel your work permit or at least nothing will happen if you dont. However, it does make things easier if you require another one later. Check with your employer, sometimes they do this for you. What ever the case it is not hard to do fill out the form hand it in and get a letter of receipt.

As your permit was based on marriage you will not have to leave the country.

I did read, (maybe here) that a new rule is being considered or introduced where you will no longer need to leave the country if you are changing jobs. I am also not sure if this applies specifically to teachers or all employment streams.

There is a difference under the 2008 Working of Aliens Act in that you can retain the WP for your records but I thought it had to be cancelled within the time frame after finishing the job nevertheless.

Hint. It is useful to keep your cancelled WPs from former jobs, in case you ever want to apply for PR or citizenship. You have to insist on getting them back or the DoE will keep them.