Yes, most US work visas require a valid job offer from a US employer. The employer must sponsor the visa and file a petition with US immigration authorities on behalf of the applicant. Without employer sponsorship, it is generally not possible to apply for work visas such as H-1B, L-1, or O-1. Some exceptional categories allow self-petitioning, but these are limited and highly selective. Securing a genuine job offer is the first and most important step in the US work visa process.