First-generation immigrants face a seniority ceiling that limits their political incorporation as candidates and officeholders. Career ladders that require qualification time in lower positions create structural barriers for this group. We use linked data from Swedish electoral ballots and administrative records to examine this idea. A novel identification strategy isolates the effect of seniority-based promotion structures from immigrant-specific disadvantages by comparing immigrants’ incorporation patterns to those of internal movers—native-born Swedes who relocate between municipalities. The seniority ceiling explains about half of the immigrant-native gap in holding political positions and almost the entire gradient of worsening incorporation at higher levels. We find strong selection effects at both the individual and group level. The seniority ceiling restricts incorporation at higher career steps for those with fewer opportunities to accumulate qualification time: those who arrived more recently or at older ages.