Short answer - you should apply using your Latvian (EU) citizenship.
Why this matters?
Universities in Latvia classify applicants mainly by citizenship/residency status, not by where they studied before. This affects:
- Tuition fees - Latvian / EU citizens often eligible for lower tuition fees. Non‑EU citizens usually pay full international student fees. So applying as an EU citizen is almost always financially more beneficial.
- Residence permits - Latvian citizenship no residence permit needed. Non‑EU citizenship requires visa + residence permit. So using your Latvian passport simplifies the process significantly.
- Even if you have graduated from a non‑EU school or currently live outside the EU you can still apply as a Latvian citizen. Your previous education credentials will still be evaluated (e.g. diploma recognition), but your citizenship determines your status.