Do I need a job offer and employer sponsor for the subclass 482 visa?

The 482 is built around employer sponsorship. You cannot apply independently; an approved business must sponsor and nominate you to fill a skilled position for which they could not find a suitable Australian worker.

The process has three parts: the business becomes (or already is) an approved sponsor, the business nominates the specific position, and then you lodge the visa application. Because the visa is tied to that sponsorship, the relationship with your employer is central to both getting and keeping the visa.