This paper analyses the impact of subnational political opportunity structures (POS)—at the electoral district level— on variations in the vote for populist radical right parties (PRRP). To this end, we analysed the aggregate vote for Vox in three national elections held in Spain in April and November 2019 and July 2023. In these elections, this PRRP broke through electorally for the first time in the Spanish political system, gaining a significant share of the vote and many seats. This support, though, varied greatly in the 52 electoral districts, which are also differentiated in terms of their magnitude and the main socioeconomic and political variables of their respective political opportunity structures. Our analysis (based on multivariate analysis) provides three relevant contributions: first, it confirms the relevance of focusing on the subnational (electoral district) level, given the district variability that may be concealed by nationally aggregated data; second, it outlines what variables best make up the subnational POS; third, and following part of the literature on electoral support for PRRP, our analysis found that nationalism and non-European immigration at the district level (together with unemployment for both 2019 elections) are the main factors explaining differences in electoral support for Vox at the district level. Medium- and long-term variables may also be relevant—although to a lesser extent— when explaining variability in support for PRRP. Interestingly, we did not find a statistically significant impact of the permissiveness of the electoral system on the vote for a PRRP.