Background: Real time ultrasound imaging (RTUI) is used to measure transversus abdominis (TrA) thickness in low back pain (LBP) populations. However, individuals with chronic low back pain (CLBP) pose specific imaging challenges, such as older age and higher body mass index, compared to asymptomatic populations or acute and sub-acute LBP groups. These challenges potentially increase measurement error and may require different imaging methods. Objectives: This review describes the methodologies and reported reliability for RTUI measurement of TrA specific to CLBP populations. Methods: A systematic database search of Medline, CINAHL, PEDro, the full Cochrane library, Scopus, and Informit identified 20 studies that used RTUI to measure TrA of CLBP participants. Two independent raters appraised the quality of the studies using the QualSyst and the QAREL critical appraisal tools. Results: Methodological quality varied from low to high. Methods for patient and transducer positioning and muscle measurement were inconsistent between studies. Eight articles cited reliability results from past studies of non-CLBP populations. Only two studies reported reliability in CLBP populations specifically and found higher Intraclass Correlation Coefficients for thickness measures at rest (0.63–0.97), compared to thickness change over time or contraction ratios (0.28–0.80). Conclusions: Inconsistency of methodology, variable methodological quality, and limited and variable reliability reporting was highlighted in this review. This LBP subgroup poses challenges for RTUI, therefore future research should include standarized methods for image acquisition. This will improve the quality of study methods, reliability of TrA measurement, and improve the applicability and comparibility of research evidence available to clinicians.