The path to an employment-based green card in the U.S. often begins with some sort of temporary, or, to use the technical term, "nonimmigrant" status. Particularly well-traveled is the path from student status (F-1) to specialty occupation (H-1B) to green card.
The main reason for this is that employers generally have little incentive to go through all the time and effort involved in bringing a foreign national to the U.S. on a permanent basis, with a green card, as described in Will Finding a Job in the U.S. Get You a Green Card?
If you're looking for a stepping stone to an employment-based green card, your best bet is a nonimmigrant visa or status that authorizes employment. One reason for this is obvious: You and your employer can check each other out through a temporary work arrangement before committing to the onerous green card application process.
A less obvious reason arises from the numerical limitations governing the yearly distribution of employment-based green cards. In many if not most cases, even after the approval of a labor certification and the employer's petition based on that labor certification, the last step of green card processing must wait for a slot to open up under the numerical limitations. (For more information about the process, see Procedures to Sponsoring a Worker for a Green Card.) An employer might be more likely to go through all this with you if you are authorized to work during this waiting time.
Two kinds of limitations apply to employment-based green cards:
The demand for employment-based green cards tends to far exceed the supply in the preference categories covering most jobs. Thus, backlogs often develop, which are worse for workers from some countries because of the historically high demand from those countries. The wait for a green card can take years, then, depending on where you're from and what kind of work you do; or sometimes there is no wait at all!
Take a look at the U.S. State Department Visa Bulletin, which is published monthly, to get a sense of the waiting times for the various categories of jobs under the numerical limitations. (A preliminary word of caution: The availability of green card slots, as reflected on the Visa Bulletin, can change in sudden, unexpected ways as immigration officials adjust their assessment of the demand in the various categories each month.)
According to the November 2019 Visa Bulletin, for example, someone from the Philippines with an advanced degree coming to the U.S. to perform a job that requires that advanced degree (a "second preference" worker) will not have to wait at all to apply for a green card, whereas an unskilled worker ("other workers") from the Philippines will have to wait almost two years. And workers from India in most categories have longer to wait than any other worker from anywhere; up to around ten years.
The more you study and follow the Visa Bulletin, the more unexpected patterns you might observe.
Relatively few nonimmigrant categories have been established to authorize employment, and each category authorizes a fairly narrow and specific type of employment. The L-1 visa category, for instance, is for intracompany transferees; R-1 is for religious workers; P-1 is for internationally recognized athletes and entertainers; and O-1 is for "persons of extraordinary ability."
The E-1 and E-2 categories are defined a little more broadly as to the work they contemplate—supervisory, executive, or specialized knowledge work. Nonetheless, the E-1 and E-2 remain relatively narrow because of specific characteristics the employer itself must demonstrate in order to employ people in the category.
The H-1B category seems fairly broad compared to these other categories, authorizing work in professional occupations requiring at least a bachelor's degree in a relevant field. The E-3 and TN categories are also for workers in professional occupations, but they are limited to people from certain countries—E-3 to Australians, TN to Canadians and Mexicans.
The H-2A and H-2B categories authorize seasonal work where labor shortages exist, and these categories contemplate unskilled as well as skilled workers—but it is virtually impossible to move from these categories to a green card.
(For complete descriptions of nonimmigrant categories, see Temporary Work Visa Options.)
Basically, your qualifications, the terms of the job offer, and the characteristics of your prospective employer will determine which of these categories, if any, you can use. You will want to study the list and investigate further if any category seems a possibility for you.
Aside from the types of work they authorize, some nonimmigrant categories are easier to use as stepping stones to a green card because Congress has specifically made them easier to use this way: Workers in H-1B or L-1 status, for instance, can extend their status beyond the ordinary limits for continuous stay in those categories if an employer has started the green card process for them.
In order to get a nonimmigrant visa, you typically have to convince the U.S. government that you intend to leave the U.S. at the end of your short stay, rather than staying on permanently. But how do you deal with the apparent conflict if you really do want to stay permanently? For the H-1B and L-1 categories, Congress has explicitly recognized "dual intent"—a rather magical concept by virtue of which you can both mean to stay only temporarily in the U.S. and to live here permanently. Dual intent is a fairly recent adaptation, in recognition of the fact that many people work in a nonimmigrant status while pursuing a green card.
For some other work-authorizing nonimmigrant categories, the law has softened the nonimmigrant intent requirement without quite reaching the outright dual intent recognized for the H-1B and L-1. With reference to E-1, E-2, P-1, and O-1 status, for example, immigration lawyers sometimes talk about "quasi nonimmigrant intent."
Though this might all sound like abstract philosophical musing, it can affect you. Once you're in the U.S. on a nonimmigrant visa, you'll find that practical consequences flow from these properties of work-authorizing nonimmigrant categories, both for your travel and for your maintenance of legal status in the United States. Be aware of the intent issue if you are using a nonimmigrant status to bridge to a green card; and consider consulting an immigration lawyer about the implications.