This study aims at validating the Staff Satisfaction Index (SSI) and the Happy Career (HC) scale for in-service firefighters. The SSI consists of two dimensions, namely, protection against hazards at work and welfare, with 16 subdimensions. A total of 6970 data points were collected via the Internet. Both dimensions of the SSI were regressed on the HC scale using partial least square structural equation modelling. The dimensions satisfied all measurements and structural model assessments. Protection against hazards at work (β = 0.370, ) and welfare (β = 0.375, ) explained 46.6% of the happiness variance. Both dimensions displayed small-to-medium effect sizes and relevance to predicting happiness (Q² = 0.339). Implications of the findings are discussed further.