I bow before the Marine. Thanks for his service. Yes the Marine can go ahead and marry whomever he wants, illegal or not, in the pursuit of his happiness. The Marine will not get in trouble for marrying someone who is illegally present in the US, especially when she is expecting the Marine's baby. The Marine should remember that having a baby on American soil does not entitle anyone to status in the US. The Marine's baby should be born in the US though, it's fitting I think. What the Marine should do though, is in my opinion, marry his beloved if that is the way he is leaning and with his marriage certificate in hand go to his C/O and ask him about PAROLE IN PLACE (PIP) in petitioning his new wife for a green card in the US. Last year the USCIS began using PIP for immediate relatives of active duty armed service people. PIP is a mechanism that essentially would allow your relative (here the Marine's wife) to be admitted or "paroled" into the US and use that admission to adjust status here in the US. In the end, with PIP it will not matter that the Marine's new wife entered the US without authorization. I would recommend that the Marine see a good Attorney to get this done. Lastly to my Marine, if I could somehow magically get a green card for your new wife to be, I would do it in a flash because I think no one deserves it more than you do for serving this country. I am not being facetious. You should be OK with the above, just develop a lot skills for patience. It could take a little time but it will be done. You are good to go! Thanks again for your service and Good Luck!
Answer Applies to: California
The marine can marry whoever he wants. His spouse may qualify for a legal status using "parole in place."
Answer Applies to: New York