Is it still possible?

THe record is in my home country, not in Thailand I should add!

99.99% sure that a police record from your home country will be needed if and when you apply.

Ah yes, but will it affect the chances of success?

In many countries a conviction will not show after a number of years on these kind of checks. It will still be in your police file but might not show on a police clearence. As every country (and state) has its on rules regrading this, the best thing to do is to ask a lawyer, your embassy or the government agency that deals with these kind of checks.

Both Thai and home country police clearances are required as part of a PR application, although Thai immigration takes care of sourcing the local one. I would have thought that any home country conviction would require at minimum an explanation and anything more than the most minor of offences would result in rejection.