Do I need a job offer in Portugal before I can apply for the D1 work visa?

The D1 is Portugal's residence visa for subordinate work — that is, working as an employee for a Portuguese employer. You cannot apply on the strength of an intention to find work; you need a concrete job already arranged.

In practice this means a written employment contract or a binding job offer that identifies both parties, is properly signed, and references the work visa or residence permit. The employer's signature is generally certified, and the offer should cover a meaningful term of employment. Without this employment relationship in place, the D1 route is not available.