A Green Card is an official document, granted to a foreign national by the United States. This document gives the holder legal rights to work, live and study, in the United States. Apart from these rights, Green Card holders are granted various other rights. You already know that there are different ways through which a foreign national can immigrate to the United States. If you are offered a job by a US employer and if the employer is ready to sponsor you, you may become eligible to get a permanent resident card or a Green Card based on employment.
However, you may become eligible to work in the United States, temporarily, if you get a work visa. In this case you may work only for one particular employer and you will have to get back to your home country after the visa expires. But you may not be required to leave the country, if you are sponsored by a US employer and if you get into the country with an immigrant visa. You may work for any US employer and remain anywhere in the country as long as you maintain your lawful status in the United States. Moreover, you will also become eligible for US citizenship, if you meet the key criteria for naturalization and if you had maintained your lawful status in the United States for five years.
You must have a permanent job in the United States if you look forward to get a Green Card based on employment. The US employer who is offering you a job will have to file an immigrant petition for you and the US employer must file Form I-140, Petition for Alien Worker. This process involves several steps and few different forms must be filed. You will have to submit supporting documents to establish your eligibility to work in the United States and the US employer also must satisfy few requirements to petition for a foreign worker.
Applying while Outside the United States
If you are outside the United States and if a US employer is ready to offer you a full time job in the United States and if he is willing to sponsor you, you will have to go through consular processing. The US employer must file Form I-140 and the US Department of State will grant you an immigrant visa after the USCIS approves the form filed by your employer. You may then travel to the United States with that visa and become a permanent resident.
Applying while You are in the United States
If you had entered the country on a temporary non-immigrant visa and if a US employer seeks to hire you, you may become a Green Card holder through the adjustment of status process. After the USCIS approves Form I-140, filed by the US employer, you may file Form I-485 for adjustment of status. You will then become eligible for a Green Card in the United States, after the approval of your application for adjustment of status and you can work and live anywhere in the country.