What is the D3 Highly-Qualified Activity visa?

Short answer: D3 is for highly-qualified professionals (PhD-level researchers, senior tech, specialists) with a confirmed Portuguese job offer.

The D3 + EU Blue Card track suits researchers, senior engineers, and ICT specialists with a Portuguese employer contract paying at least 1.5× the national average (~€2,400/month gross). It's typically faster at AIMA than D7/D8 and converts cleanly to permanent residence at year 5. Compare routes in Visa Advisor.