Changing jobs on an H-1B visa is called an H-1B "transfer" (technically a new petition by the new employer). Thanks to H-1B portability (AC21), you can begin working for your new employer as soon as USCIS receives the transfer petition — you don't have to wait for approval.
Key Takeaway
You can start working for the new employer once USCIS receives the petition (receipt notice). The new employer files a new I-129 petition. If you have a pending green card (I-140), your priority date is portable to the new employer after 180 days.
Requirements
You must currently be in valid H-1B status, the new position must qualify as a specialty occupation, the new employer must file a Labor Condition Application (LCA) and I-129 petition, and you must not have any gaps in your H-1B status. Premium processing ($2,965) is recommended for faster resolution.
Green Card Portability
If your I-140 has been approved for at least 180 days, your priority date and approved petition are portable — your new employer can continue the PERM/green card process without starting over. This is critical for anyone in the EB-2/EB-3 backlog.