Background: In the Alentejo region, population aging increases the risk of functional decline, loneliness and poorer quality of life (QoL) among community-dwelling older adults. Senior centers are community services designed to mitigate these risks, but evidence on users’ profiles remains scarce. Objective: To characterize functioning, QoL and loneliness among users of senior centers and examine their interrelations. Methods: Cross-sectional study with a convenience sample of senior center users in Évora, Portugal. Data were collected on sociodemographic, cognitive performance (MMSE), functioning (Elderly Nursing Core Set, ENCS), loneliness (UCLA-LS-16) and QoL (WHOQOL-BREF; 0–100). Associations with QoL were analyzed using Spearman’s and partial correlations adjusted for age, gender and education, with multiple testing controlled using the Benjamini–Hochberg correction. Results: Participants (n = 45) showed preserved overall functioning, with at most mild problems in self-care, communication and mental functions, and moderate-to-high QoL. The ENCS Relationships domain was the most consistent correlate of QoL (ρ =  − 0.42; q = 0.025), and this association strengthened after adjustment (ρ_partial =  − 0.49; q_partial = 0.003). Loneliness showed a small negative association with QoL in bivariate analysis, but this was not statistically robust after correction. Conclusions: Among senior center users, QoL appears more closely related to perceived functional support in relationships (family, peers, caregivers and professionals) than to loneliness per se. Strengthening and qualifying formal and informal support networks may have greater impact on QoL than actions focused solely on reducing loneliness. Larger, multicenter and longitudinal studies are needed to test these hypotheses and improve generalizability.