The objective of our overview of systematic reviews was to critically analyze the evidence from existing systematic reviews investigating the effectiveness and safety of low-level laser therapy (LLLT) in patients with breast cancer-related lymphedema (BCRL). In addition, an updated and comprehensive systematic review was conducted, which aimed to provide updated evidence about this topic. PubMed, EMBASE, and Cochrane Library databases were systematically searched for systematic reviews and randomized controlled trials (RCTs) investigating the effectiveness and safety of LLLT in patients with BCRL. The methodological quality for each of included systematic reviews or RCTs was assessed using the Assessing the Methodological Quality of Systematic Reviews 2 (AMSTAR 2) tool or Cochrane risk of bias tool, respectively. The updated systematic review separately compared the effectiveness of LLLT to each of active or negative interventions. Data were pooled with random-effects models for each outcome per comparison. The evidence quality of outcomes was assessed using the Grading of Recommendations, Assessment, Development and Evaluation (GRADE) or GRADE-Confidence in the Evidence from Reviews of Qualitative research (GRADE-CERQual) for quantitative studies and qualitative studies, respectively. Seven systematic reviews and ten RCTs met the eligibility criteria. Conflicting results regarding the effectiveness of LLLT were presented by the overview of systematic reviews. The AMSTAR 2 showed that the methodological quality of included systematic reviews was low or critically low quality due to one or more critical weaknesses. The GRADE and GRADE-CERQual showed that the evidence quality was low to very low for most outcomes. The updated systematic review showed that LLLT may offer additional benefits as compared to compression therapies (pneumatic compression or compression bandage), placebo laser, or no treatment for patients with BCRL. However, when compared to other types of active interventions, LLLT did not improve outcomes significantly. None of the treatment-related adverse event was reported. Many trials had a high or unclear risk of bias for two or more items, and our updated systematic review showed low quality of evidence per outcome using GRADE approach. Due to insufficient data and poor quality of evidence, there is uncertain to reach these conclusions that LLLT is superior to another active or negative intervention and is safe. More RCTs of high methodological quality, with large sample sizes and long-term follow-up, are needed to inform clinical guidelines and routine practice.