Mechanical low back pain (LBP) is a very common, expensive, and significant health issue in the western world. Functional musculoskeletal conditions are widely thought to cause mechanical low back pain. The role of foot posture and leg length discrepancy in contributing to abnormal biomechanics of the lumbopelvic region and low back pain is not sufficiently investigated. This critical review examines the evidence for the association between foot function, particularly pronation, and mechanical LBP. It also explores the evidence for a role for foot orthoses in the treatment of this condition. There is a body of evidence to support the notion that foot posture, particularly hyperpronation, is associated with mechanical low back pain. Mechanisms that have been put forward to account for this finding are based on either mechanical postural changes or alterations in muscular activity in the lumbar and pelvic muscles. More research is needed to explore and quantify the effects of foot orthoses on chronic low back pain, especially their effects on lumbopelvic muscle function and posture. The clinical implications of this work are significant since foot orthoses represent a simple and potentially effective therapeutic measure for a clinical condition of high personal and social burden.