I'm reading about the K-1 fiancé(e) visa available to foreign nationals planning to marry a US citizen within the US, and am wondering if its required for someone who has other legal means of entering the US? Specifically, for an EU citizen who can enter the US under the VWP, should a K-1 application still be done? Or is the K-1 simply for those who have no other legal means to enter the country?
The answer is No, it is not required. However, in most cases there is no other legal way for an alien fiancé who is not a permanent resident to enter the U.S. for the purpose of staying in the U.S. permanently. (I am assuming the question is about fiancés who intend to immigrate to the U.S., because that's what K-1 is for. If one only intends to get married during a brief trip to the U.S. and then leave, then VWP or B-2 visa is appropriate.)
The fiancé is not eligible for an immigrant visa, because he/she is not married yet and thus not yet a relative. And most categories of non-immigrant visa (and VWP) require the holder to not have preconceived intent to immigrate using that visa (i.e. not intend to stay and apply for Adjustment of Status during that entry) both when applying for the visa and when using it to enter the U.S. This includes categories like B visas (tourist or business visa), F visas (student visa), and most other types. So these visas cannot be used when one intends to stay. (One could intend not to stay when entering, and change their mind later, but since you're asking this question at this stage, I'm assuming you have a preconceived intent to stay.)
There are a few types of non-immigrant visa that don't have this requirement of not intending to use it to immigrate. This includes the K (fiancé) visa itself, as well as H and L work visas. So if you are a fiancé and, for example, are working on an H or L work visa, then yes, you can feel free to use that to enter the U.S. for the purpose of getting married and applying to immigrate, without getting a fiancé visa. But in all other cases, you will have to get a fiancé visa (or marry outside the U.S.).
The answer is depends.
I would suggest that you consult the immigration lawyer before attempting anything other then the K-1 route if you intend to get married.
As was explained to me by a lawyer awhile back if the entry of a foreigner you have married under a B1/B2 or VWP is suspected to be for the purpose other then tourism you could have problem with CIS during the adjustment of status process.
Having said that, I am aware of multiple cases where a person had entered the United States under the B1/B2, got married several months after that entry and received Permanent Residency in the United States through adjustment of status, so yes using VWP may be possible but again consult a lawyer.
My husband was in the US for two years before we met on an over-stayed H2B visa. After we met and dated, we lived together on and off for about 10 years and finally decided to get married. He was able to get an adjustment of status no problems. But...his H2B allowed him to work for three months when he first came here and get a social security card (only one that allowed him to work with a work permit) and a driver license. He was able to work with that Social Security Number and he paid taxes on everything he earned for the entire time he worked, even though he had over-stayed. We had to have a lot of proof for our interview after marriage. Tons. So, I'm not recommending anything here, just saying, it was better that we had a long term relationship before we went to our interview.