First, let’s clarify the terminology. As you can see from other questions on this page, there is an important distinction between visa and status. If you really are talking about visas then the answer is that visas can never be “converted”. It would also be pointless to do so, since a visa is useless inside the USA. You would have to apply for a completely new one at a US consulate. Having a tourist visa in your passport won’t usually make a difference when you apply for another type of visa.
But most people asking this type of question are actually referring to changing from tourist status rather than from a tourist visa. In this case, the answer is complex and depends on a number of details.
First of all, you need to check whether you arrived in the USA with a tourist visa, or on the visa waiver program. That’s pretty easy to figure out. Look at the I-94 card in your passport. If it is green, you have a visa waiver. If it is white, you have an actual tourist visa.
With the visa waiver, there is no way you can change to *any* other status (except for “spouse of US citizen”). You would have to leave the USA before your 90 days are up and apply for a new visa of the appropriate category at a US consulate abroad. If you have a white I-94, you may be able to change status without leaving the USA. The next thing you need to figure out is which status you want to change to. There is no such thing as a “generic working status” but there are quite a few individual categories that would allow you to work. Realistically, you would only be able to get a non-immigrant working status. In all cases, you would first have to find an employer willing to sponsor you. The employer would then file almost all the paperwork, and guide you through the remainder. With any of these categories, you would be allowed to work only for the sponsoring employer.
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