Among 5,368 UK adults with depression followed for 12 years, adherence to Mediterranean diet, DASH, and HEFI-2019 patterns each reduced all-cause mortality by 8-10% per quintile increase. The Mediterranean diet and HEFI-2019 showed the strongest protective effects, with HEFI-2019 specifically reducing cardiovascular death risk by 21% per quintile. Key protective components included higher fish intake and lower consumption of refined grains, added sugars, and sodium. This represents a significant finding in psychiatric epidemiology, as depression typically doubles mortality risk through complex pathways involving inflammation, medication side effects, and lifestyle factors. The protective magnitude—comparable to that seen in general populations—suggests dietary interventions could substantially improve outcomes in this vulnerable group. However, the observational design cannot establish causation, and the relatively short follow-up may underestimate long-term benefits. The study's strength lies in its large, well-characterized cohort and comprehensive dietary assessment using multiple validated patterns. For clinicians, these findings support integrating nutrition counseling into depression care, potentially offering a practical, accessible intervention to complement traditional treatments and address the elevated mortality burden in psychiatric populations.