Previous cross-sectional studies have reported associations between self-compassion, self-criticism, and positive body image, yet prospective studies establishing the temporal order of these relationships are missing. The present study sought to clarify the nature of these associations by investigating possible longitudinal bi-directional links between self-compassion, self-criticism, and three components of positive body image (body appreciation, functionality appreciation, and body image flexibility). Data were analyzed from 2982 adult women who completed survey instruments at baseline (T0), four-month follow-up (T1), and eight-month follow-up (T2). Attrition rate ranged from 0–56% across time-points. Cross-lagged panel models were computed to test for bidirectional associations. We found evidence of reciprocal, negative associations between self-criticism and the three components of positive body image across the three time-points. We also found evidence that T0 self-compassion predicted increased body image flexibility and functionality appreciation at T1 (paths were non-significant from T1 to T2), whereas T0 body appreciation predicted increased T1 self-compassion (but was non-significant from T1 to T2). Findings suggest that compassionate and uncritical ways of responding to the self may be relevant precursors and outcomes to positive body image, depending on the timing of assessment, highlighting viable targets for intervention.