Objectives The present study aimed to determine the effects of motivational interviewing (MI) on treatment outcome as measured by variations within glycosylated hemoglobin (HbA1c) and depression in cases subject to type 1 diabetes mellitus (T1DM). Methods Two independent investigators electronically conducted a literature search by exploiting Cochrane Library, EMBASE, PubMed, Google Scholar, and ClinicalTrials.gov from inception to January 2021. Randomized controlled trials and quasi-experimental interventions were involved, in which motivational interviewing was examined to be associated with the treatment outcome in people with T1DM. We calculated standard mean difference (SMD) with 95% confidence intervals (CIs) using a random-effects model by RevMan V 5.4.1 software. Results Lastly, a total of 9 studies comprising 1322 (680 vs 642) cases were covered, 3 of which involved 332 (166 vs 166) cases for depression meta-analysis. The analysis indicated a 0.11% improvement in glycemic control in populations having accepted a MI intervention in comparison with usual care participants, whereas the effect did not show statistical significance (SMD, - 0.11; 95% CI, - 0.33 to 0.11; Z = 0.97, p = 0.33, I-2 = 60%). The depression scores between the intervention group and the control showed no significant difference (SMD, - 0.00; 95% CI, - 0.93 to 0.92; Z = 0.00, p = 1.00, I-2 = 91%). Conclusions The effect of motivational interviewing in reducing glucose levels and depression is suggested to be limited. But as impacted by the issues of heterogeneity and small number of included studies, caution in interpreting the present findings is advised.