This longitudinal study investigates how work-related well-being measured by job satisfaction differs by employment types in Korea. The relationship between job satisfaction and employment type reflecting internal (motivation of choice) and external (type of employment contracts) heterogeneity of non-standard workers is examined. The first 6th wave (2009–14) of the ‘09 sample’ from the Korean Labour and Income Panel Study (KLIPS) is used. The results show that average level of job satisfaction of non-standard workers is lower than that of standard workers and the change in employment type from standard to non-standard leads to a decrease in job satisfaction. Examining the internal heterogeneity of non-standard workers shows job satisfaction did not decrease for those who voluntarily choose non-standard contracts but did decrease for the involuntary group. Moreover, external heterogeneity did not affect those who involuntarily chose non-standard contracts, but the outcome varies for the voluntary non-standard workers.