Examining the rising prevalence of subjective cognitive decline as an early indicator of dementia in adults, this study investigates its complex interaction with loneliness and quality of life in individuals with preclinical dementia. Using a convergent parallel mixed-method approach, we employed Structural Equation Modeling on a cohort of 149 older adults. Qualitative insights were derived from focused group discussions and in-depth semi-structured interviews with a cohort of 23 older adults. Loneliness emerges as a pivotal contributor, exerting a discernible partial indirect effect on quality of life through subjective cognitive decline (indirect effect = −0.145, p = .006). Noteworthy differentials surfaced, with the impact of subjective cognitive decline on quality of life heightened in those with chronic diseases (△ χ2 = 6.139, p = .013). Loneliness, wielding a palpable impact, intricately interlaces with quality of life, the nexus of which is intricately mediated by subjective cognitive decline.