Loneliness is highly prevalent globally and has been noted in all age groups. Loneliness is associated with significant physical and mental health risks. These individuals have a poor quality of life. Lonely individuals also demonstrate a high mortality rate and incur more health care costs. Type 2 diabetes mellitus (T2DM). a common chronic disease. Worldwide, it is expected to affect 629 individuals in 2045. Several studies have established an incriminating role of loneliness in the pathogenesis and progression of T2DM. It is estimated that the risk of developing a high HbA1c is almost fivefold in lonely people. This increased risk is independent of other confounding factors. Although increased inflammation and reduced immunity play a role, the main mechanism appears to be an increase in the hypothalamic-pituitary adrenocortical activity. Loneliness also increases unhealthy lifestyles, which also contribute to this deleterious loneliness-diabetes link. Lonely people are also more burdened with chronic diseases, which further increase the diabetic risk and its worsening. They also tend to be more non-adherent to healthcare recommendations. On the other hand, diabetic patients face a multitude of issues with daily living and healthcare, and these tend to increase loneliness. The causative factors and their mechanisms underlying this bidirectional relationship between loneliness and T2DM is narratively reviewed in this manuscript.