Aim Low back pain (LBP) resulting from degenerative lumbar spine disease is a leading contributor to global disability. Changes in the morphology of the lumbar multifidus muscle on magnetic-resonance imaging (MRI) are associated with worse LBP and disability, but the association between multifidus morphology and post-operative outcomes is not known. The purpose of this systematic review is to examine the relationship between pre-operative multifidus morphology and postoperative changes in pain and disability. Methods We performed a systematic search using the Cochrane Library, EMBASE, MEDLINE, CINAHL and Scopus databases covering the period from January 1946 to January 2018. The literature was searched and assessed by independent reviewers according to the Preferred Reporting Items for Systematic Reviews and Meta-Analysis (PRISMA) statement. All relevant papers were assessed for risk of bias according to the Quality in Prognosis Studies tool. Results The initial search yielded 436 studies, of which 6 studies were included in the analysis. Four studies were at a low risk of bias. These studies included a total of 873 patients undergoing spinal surgery. An association between low fat infiltration and greater improvement in LBP and disability following surgery was identified. There was insufficient evidence to identify a relationship between cross-sectional area (CSA) and LBP or disability. Conclusions This systematic review found evidence for an association between low multifidus fat infiltration on MRI at baseline and greater reductions in measures of LBP and disability following surgical treatment. There is also limited evidence for an association between larger pre-operative multifidus CSA and improvements in disability, but not pain. The findings of this review should be interpreted with caution due to the small quantity of the available literature.