If an eligible dependent is in the U.S., the dependent family member(s) would file a Form I-539 with USCIS prior to the end date of the current immigration status to obtain/extend H-4 status in U.S. Usually, H-4 applications are submitted to IC at the same time as an initial or extension H-1B requests. However, dependents (spouses and unmarried minor children (under 21 years of age)) who are eligible for H-4 status may apply for H-4 status at any time on their own, after the principal has obtained H-1B status.
If an eligible dependent is outside the U.S., dependent(s) must apply for an H-4 visa stamp outside the U.S. (Canadian citizens may be exempt) with the documents of the main beneficiary to be able to enter the U.S. in an H-4 dependent visa status.
Please note, the H-4 dependent(s) Form I-539 is a self-application, employee and his/hers dependent(s) are responsible for making sure that the application is complete and signed correctly and all fees and documents are included. If you need an Immigration attorney assistance with H-4 application, please let H-1B advisor know and request a contact information for an immigration attorney to obtain a fee quote and for help to prepare H-4 Form I-539 application for dependent(s).
As a courtesy, IC can submit the H-4 dependent(s) I-539 application along with the I-129 petition for the H1B principal applicant.
Please follow the instructions found at Instructions for Form I-539.
Additional information can be found at https://ic.uci.edu/h-4-dependents