I will file taxes jointly with my nonresident alien spouse. I will attach the necessary statement but also want to know if we both can contribute to a Backdoor Roth IRA.

@sebastianf10-gma , for your Non-Resident Alien and working for a Foreign Govt. institution,   there are few things to consider :

(a) generally  while  an NRA or US Person works for  a Foreign Govt.,  ( ie.,e. in a Consulate/ Embassy )  the  income  is not taxed by the USA under  international; norms ( I am not sure but I think it is  pursuant to  Basel Agreement.

(b)  However, US citizens/ Persons still are  subject to  SEC A ( Equivalent of FICA  at 15.3 % but with no employer participation ) --  they often have to file a Schedule-SE to pay the  SECA.

(c)  The  States may or may not  hold these employees  ( NRAs ) immune  from State taxes   ( Tell me the state you live in and I can look up  ).

Thus , if you both agree  for your spouse to be treated as a Resident for Tax purposes,  you will be exposing her salary to both  Federal  and State Taxes  , in addition to  SECA.  The benefit of a larger standard deduction and ability to participate in  IRA contributions etc.  may not be enough to  offset the tax implications.

I would highly recommend that you use  a CD/ Download version of TurboTax ( my favorite being  Home & Business  because  of  ability to handle complex situations ) and try out what-if scenarios.  This will indeed allow you to see the impacts of such a decision.

If you proceed on this path  -- 

1. Her first day as a resident would be the first day present in the USA   and if this results in the full 365 days then  the standard deduction is available to both -- else  you must use itemized deduction

2. You prepare your return using both  TINs ( SSN or ITIN ). 

             If she does not have an ITIN, then you need to add  that application  along with your  return .   Note that in such a case you have  to prepare the return with a dummy  TIN, then print the return and replace the  TIN with " NRA".  The application -W-7 along with all the documents required   -- see  here -->

  About Form W-7, Application for IRS Individual Taxpayer Identification Number | Internal Revenue Service

             If he does have a TIN then  you are all set.

3. You then have to print the return, sign date  ( both spouses )  

4.  You then include a letter signed and dated by both the spouses requesting that the NRA spouse be treated as a Resident for Tax Purposes.

5. You now need to  send all these  documents along with your return to the IRS and the State   ( along with a copy of the federal return ). Please use a mail service like  UPS / FedEx so the delivery can be traced.   IRS will generally grant ITIN retroactively. 

Obviously this being by mail and the requests to be processed , it is going to take a while to hear back from the IRS.

Does this make sense ?

Is there more one of us can do for you ?

pk