Background: Smartphone addiction (SA), characterized by excessive and uncontrolled use, poses significant physical, psychological, and social challenges, particularly among university students. In Bangladesh, where SA prevalence reaches 61.4% among young adults, socio-economic stressors, lifestyle factors, and mental health issues amplify risks. This study investigates SA prevalence and its associations with socio-economic, physical, and psychological conditions among university students, addressing a critical gap in developing country contexts. Methods: A cross-sectional survey was conducted at Noakhali Science and Technology University, Bangladesh, involving 450 students from four faculties. Data were collected using a structured questionnaire, including the Smartphone Addiction Scale-Short Version (SAS-SV) for SA (cutoffs: ≥31 males, ≥33 females), and self-reported measures for sleep, physical activity, sedentary behavior, and psychological conditions (anxiety, depression, stress, worry). Chi-square tests and logistic regression analyzed associations and predictors, with p<0.05 for significance, using SPSS v27. Results: SA prevalence was 63.8% (286/450), with males (75.5%) showing higher rates than females (50.7%, AOR=0.19, p<0.001). Significant associations were found with academic year (4th-year: 75.7%, χ²=16.63, p=0.002), faculty (Social Science: 72.7%, χ²=15.59, p=0.001), paternal education (secondary: AOR=19.21, p<0.001), financial dependency (AOR=0.26, p<0.001), sleep (<5 hours: 87.7% addicted, χ²=188.50, p<0.001), physical activity (4–5 times/week: AOR=0.07, p<0.001), and psychological conditions (e.g., anxiety nearly every day: AOR=46.34, p<0.001; worry: AOR=253.40, p<0.001). Psychological factors were the strongest predictors, explaining 49.5–67.8% of SA variance. Findings align with local studies (61.4% prevalence) but exceed global estimates (23.3%). Conclusion: High Smartphone addiction prevalence among Bangladeshi university students is driven by psychological distress, socio-economic constraints, and lifestyle factors. Interventions should prioritize mental health support, promote moderate physical activity, and address socio-economic stressors through awareness and counseling. Longitudinal studies are needed to clarify causal pathways.