Background: Although income level may play a significant part in mortality among migrants, previous research has not focused on the relationship between income, migration and mortality risk. The aim of this register study was to compare all-cause mortality by income level between different migrant groups and the majority settled population of Finland. Methods: A random sample was drawn of 1,058,391 working age people (age range 18–64 years; 50.4% men) living in Finland in 2000 and linked to mortality data from 2001 to 2014. The data were obtained from Statistics Finland. Cox proportional hazards models were used to investigate the association between region of origin and all-cause mortality in low- and high-income groups. Results: The risk for all-cause mortality was significantly lower among migrants than among the settled majority population (hazards ratio (HR) 0.57; 95% confidence interval (CI) 0.53–0.62). After adjustment for age, sex, marital status, employment status and personal income, the risk of mortality was significantly reduced for low-income migrants compared with the settled majority population with a low income level (HR 0.46; 95% CI 0.42–0.50) and for high-income migrants compared with the high-income settled majority (HR 0.81; 95% CI 0.69–0.95). Results comparing individual high-income migrant groups and the settled population were not significant. Low-income migrants from Africa, the Middle East and Asia had the lowest mortality risk of any migrant group studied (HR 0.32; 95% CI 0.27–0.39). Conclusions: Particularly low-income migrants seem to display a survival advantage compared with the corresponding income group in the settled majority population. Downward social mobility, differences in health-related lifestyles and the healthy migrant effect may explain this phenomenon.