Hi Guys,
I got married in 2013 but at that time my wife was not here in US and I didn't have her ITIN so I filed as single. Now, since she got her SSN, I want to file tax ammendment as married.
What should be the reason I mention for this in the 1040x (exact wording please)? Also,should I file as married filing joint or married filing separate? and should i include any supporting documents (like marriage certificate) as well?
Thanks.

married filing separate you give up certain tax deductions and benefits.. So it might be better you file married filing joint... I dont think its necessary to include supporting documents.. Depending on how complicated your tax returns since 2013 was... you have to do more research and/or talk to tax specialist on this. If your tax return was some simple stuff.. probably no need for tax specialist..

Did you have children in 2013?

For good excuse : my spouse did not have earning , did not realize I have to file mfj.

Thanks Mojaboy, mine is simple, no complicated stuff.I talked with a tax guy but he doesn't have much idea about whether to include marriage certificate since it was issued from Nepal. He told me to married filing joint though.
Magorkhei bro, I don't have children.

You can amend the Tax return with married filing joint .Just write I'm amending to change my filing status from single to Married filing joint .At that time my wife didn't have social security issued by Social security Administration .

Also don't get confused with marriage certificate or birth .SSA reports everything to IRS so they know they know they know .

My wife was not here and she did not have ss number is the worst reason , you can not file tax for a person who was not here for a single day in tax year  and did not have social number.
For that reason i put simple reason as if you did not know much about tax.

Guys, any other suggestions please?

Tell the truth.