<p>Loneliness and multimorbidity are well-established correlates of Quality of Life (QoL) in later life, yet little is known about how they shape longitudinal trajectories of QoL rather than average levels. This study aimed to identify distinct QoL trajectories in later life and examine whether baseline loneliness and health-related vulnerability differentiate these pathways. Data were drawn from the English Longitudinal Study of Ageing (ELSA), a nationally representative cohort of adults aged ≥ 50 years. QoL was assessed using the CASP-12 scale across Waves 2–9. Latent class mixed models were used to identify distinct QoL trajectories over time. Multinomial logistic regression examined associations between baseline loneliness, multimorbidity, and sociodemographic characteristics with trajectory membership. Sensitivity analyses were conducted using alternative baseline waves to assess robustness. Three distinct QoL trajectories were identified: stable high, declining, and improving. Older age, multimorbidity, lower wealth, and higher loneliness were associated with increased likelihood of belonging to both declining and improving trajectories relative to the stable high group, indicating greater QoL instability rather than a single direction of change. Loneliness showed the strongest association with trajectory membership, with low loneliness strongly protective against deviation from stable high QoL. The trajectory structure remained consistent across sensitivity analyses. QoL in later life follows heterogeneous and dynamic pathways. Loneliness and health-related vulnerability primarily distinguish individuals experiencing instability in QoL rather than inevitable decline. These findings suggest that loneliness may represent a promising target for intervention aimed at promoting stability and resilience in later-life QoL.</p>