Abstract: Psychological well-being and the satisfaction of basic psychological needs are key indicators of mental health and personal resilience. The relevance of this study stems from the need to identify factors influencing these indicators amid the growing phenomenon of social loneliness. Loneliness is associated with deficits in relatedness, lowered self-esteem, reduced motivation, and diminished psychological integration, making it a critical issue for psychological prevention. The study aims to identify differences in levels of psychological well-being and basic psychological needs satisfaction among individuals with varying degrees of loneliness, as well as to establish correlations between these variables. The sample consisted of 216 participants aged 19 to 60, of whom 91.7% were women and 8.3% were men. The following psychological assessment tools were used: Ryff’s Psychological Well-Being Scale (RPWB), the Basic Psychological Needs Satisfaction Scale (BPNSS), Beck’s Hopelessness Scale (BHS), and the Loneliness Experience Questionnaire (Manakova). Statistical analysis included the Shapiro–Wilk test, the Mann–Whitney U-test, and Cronbach’s alpha for reliability estimation. Statistically significant differences were found in psychological well-being and basic needs satisfaction between groups with moderate and high levels of loneliness. Individuals with higher loneliness scores demonstrated notably lower indicators across all well-being and needs satisfaction scales. Positive correlations were also found between the satisfaction of basic needs and all components of psychological well-being. The study is the first to reveal statistically confirmed differences in psychological well-being and basic needs satisfaction depending on the degree of loneliness. The novelty lies in establishing the role of basic needs as mediators in the negative psychological impact of loneliness. The findings confirm that the intensity of loneliness has a broadly negative effect on psychological functioning, reducing internal resilience, motivation, and social adaptability. Satisfaction of basic needs—especially autonomy and relatedness—serves as a protective factor supporting well-being. The results can inform the development of psychological support programs aimed at strengthening internal resources and preventing emotional disturbances associated with loneliness.