I'm going to Singapore for business purposes in a few weeks, and I'd like to get a Non-Immigrant Visa (Type O?). Me and my fiance are getting married soon (but not yet), and I'd like to get my Non-Imm O visa now so I could extend it here once I am married and can show the 400k in my bank account.

It is my understanding that in order to obtain a O visa you need to apply for either:

-Being married to Thai National

-Wishing to retire and over 55yo (or 50yo?)

Since I'm not married now and under 50yo, can I still apply for a Non-Imm O visa for other purposes such as getting married soon? And is it safe to apply for such a visa since I'll be in Singapore only for 2 days, so if my visa is refused im going to have to come back on a 30 day stamp

My fiance will be traveling with me, can this be of any help? Thanks!

You are not likely to obtain a non immigrant O visa on that basis but you can ask first. Your best plan might be to obtain a tourist visa as that can be changed to non immigrant inside Thailand for support Thai wife extension of stay. If not, or you are too late to change the tourist visa, you can exit with copy of wife ID card and the marriage certificate to obtain a non immigrant at the closest Consulate and do your extension from that.

...

-Wishing to retire and over 55yo (or 50yo?)

...

50 yo it is.