In theory, fiancés have the right to work in the United States during the 90-day duration of their visa. In practice, taking advantage of this right is more difficult than it sounds -- close to impossible, in fact.
As a K-1 visa holder, you can work in the United States only if, after entering, you apply for and receive a work permit. This is known by U.S. Citizenship and Immigration Services (USCIS) as an Employment Authorization Document or EAD. It is a small plastic card with your photo on it. For application procedures, see below; but first, keep reading for the reasons you might not want to apply.
Timing Problems With Applying for a Work Permit
The difficulty with applying for a work permit is that the USCIS Service Centers routinely take from 45 to 90 days to issue them. This means that your chances of receiving your work permit while you are still eligible for it, as the holder of a fiancé visa, are slim.
You would likely be better off marrying as soon as possible and focusing on preparing your adjustment of status (green card) application. As part of your application packet, you can include a Form I-765 requesting a work permit. In fact, you won't have to pay anything extra for it if it's included with your adjustment packet -- as contrasted with applying while you are still only in fiance visa status, in which situation you would have to pay a separate USCIS fee.
Once you submit your adjustment of status application, you will still probably wait anywhere from 60 to 90 days for your work permit. You can check the "USCIS Processing Time Information" page of the agency's website to find out how long other I-765 applications are taking at the time that you file yours. Click "National Benefits Center." That is where your work permit application will b processed, despite the fact that you will be interviewed for your adjustment of status application at a local USCIS office.
How to Apply for a Work Permit as a K-1 Fiance Visa Holder
If you still want to apply for a work permit, use Form I-765, Application for Employment Authorization, available for free download from the USCIS website.
Go straight to the last page of the form. This is the only page that you will have to submit.
Assuming this is your first work permit, under “I am applying for,” check “Permission to Accept Employment.”
Questions 1-14: Self-explanatory.
Question 15: You are a “K-1 Visa-holder.”
Question 16: Your eligibility category is (a)(6) as a fiancé. Sign your name in the section titled “Certification.” The following section is only for use by lawyers, paralegals, or anyone else who filled out the form for you.
When finished, mail the form, the fee ($380 as of early 2015), two passport-style photos, and proof of your fiancé visa status (such as a copy of your approval notice, the stamp in your passport, and your Form I-94) to the appropriate USCIS Service Center, as indicated on the USCIS website.
Alternatively, you can file your Form I-765 electronically, through the USCIS website. However, you will still need to mail your supporting documentation to USCIS (using the address that you’ll get in your confirmation receipt). Complete instructions for “E-Filing” can be found on the USCIS website (when you go to the page to download the form, click “Instructions for Electronically Filing Form I-765” under “File Online”).
After sending it in, you'll wait. And no matter how long USCIS takes to approve it, the EAD will expire along with your K-1 status.