The manuscript has been initially submitted in April 2022. A revision has been submitted in February 2023. The paper was finally accepted for publication in *Psychological Bulletin* in May 2023. All files in this repository are licenced under the terms and conditions of the Creative Commons CC-BY 4.0 license. **Abstract** How does subjective well-being (SWB) develop across the lifespan? Theories and previous empirical research suggest heterogeneous conclusions regarding this question. Therefore, in this meta-analysis, we synthesized the available longitudinal data on mean-level change in three SWB components: life satisfaction, positive affect, and negative affect. The analyses were based on 443 unique samples with a total of 460,902 participants. Our results showed that life satisfaction decreased from age 9 to 16 (*d* = -0.56), increased slightly until age 70 (*d* = 0.16), and then decreased again until age 96 (i.e., the oldest age for which data on life satisfaction were available; *d* = -0.24). Positive affect declined from age 9 for almost the entire time until age 94 (*d* = -1.71). Negative affect showed small ups and downs between ages 9 and 22. After age 22, negative affect declined until age 60 (*d* = -0.92), after which it increased again until age 87 (*d* = 0.58). Average changes in positive and negative affect were stronger than in life satisfaction. The moderator analyses suggested that the pattern of mean-level changes held across gender, country, ethnicity, sample type, measure of SWB, time frame of SWB measure, and birth cohort. In sum, we found a favorable developmental trajectory of SWB over large parts of life for life satisfaction and negative affect and decreases from childhood until late adulthood for positive affect. In late adulthood, SWB tended to worsen rather than improve. Consequently, interventions aimed at maintaining or enhancing SWB in older adults might be useful.