Good psychological well-being contributes to a satisfying life, reduces loneliness, and enables a better quality of life. Due to the COVID-19 pandemic, people worldwide have faced various challenges, which manifest in mental health problems, dissatisfaction with life and increased loneliness. This study aimed to investigate the influence of loneliness on mental well-being and life satisfaction among the adult population during the COVID-19 pandemic. A cross-sectional study was conducted between October 2021 and January 2022. A total of 664 participants took part in the survey, of whom 484 (73%) were female and 180 (27%) were male. Our results show that loneliness can explain 48% of the total variability in mental well-being and 52% of the variability in life satisfaction. The results show a higher level of loneliness and use of information and communication technology and a lower level of contact with relatives and friends, life satisfaction, and well-being during COVID-19 than they considered before the time of COVID-19. Study findings can help improve loneliness and mental well-being, and, consequently, life satisfaction.