Background: Happiness and life satisfaction are core dimensions of subjective well-being. The 3-item Satisfaction With Life Scale (SWLS-3) was developed as a brief alternative to the original 5-item SWLS (SWLS-5) but lacks validation in Italian samples. Objective: To evaluate the psychometric properties, reliability, and construct validity of the Italian SWLS-3 versus the SWLS-5. Methods: A community sample of 504 Italian adults (Mage = 35.15, SD = 12.31~ 82% female) completed the SWLS-5, SWEMWBS, and DASS-12 online. Confirmatory factor analyses examined unidimensionality; internal consistency employed Cronbach's α and McDonald's ω. Convergent and discriminant validity were tested via correlations and HTMT ratios. Results: Both scales showed excellent fit; the SWLS-3 was slightly superior (CFI = 0.972, RMSEA = 0.069) to the SWLS-5 (CFI = 0.963, RMSEA = 0.070). Reliability was high for both (α = 0.881–0.897; ω = 0.876–0.896). The SWLS-3 correlated strongly with the SWLS-5 (r = .949), positively with mental well-being (r = .654), and negatively with distress (r = -.483). HTMT values supported discriminant validity. Conclusion: The Italian SWLS-3 demonstrates excellent psychometric performance and is recommended as a time-efficient screening tool in clinical and large-scale epidemiological research, though some researchers may still prefer the full version.