Introduction: Extramural vascular invasion (EMVI) has been recommended as an independent prognostic factor for poor overall survival rate in rectal cancer and can be used as a potential biomarker. Early prediction of prevalence of synchronous metastasis can elevate the disease-free survival rate. We aimed to evaluate the magnetic resonance imaging (MRI)-detected EMVI (mrEMVI) scoring system in predicting distant metastasis in T3 rectal cancer. Methods: Patients with postoperative histopathologically confirmed T3 rectal cancer without previous treatment from July 2014 to December 2015 were enrolled in this study. Two blinded radiologists evaluated mrEMVI status. mrEMVI was categorized as EMVI-positive or EMVI-negative in T2-weighted images using an mrEMVI scoring system. The results, along with other clinical characteristics (age, sex, tumor location, MRI-detected distance of mesorectal extension, lymphatic invasion, perineural invasion, mrEMVI score, and carcinoembryonic antigen [CEA]), were then correlated with synchronous metastases to determine the risk factors using univariate and multivariate analysis. Results: Of 180 patients, 38 were confirmed to be mrEMVI-positive, 142 mrEMVI-negative. There were 34 patients with synchronous metastasis, of whom 25 were mrEMVI-positive and 9 were mrEMVI-negative. Three factors were significantly associated with synchronous metastasis: mrEMVI (p = 0.001; odds ratio = 8.665), histopathologic lymphatic invasion (p = 0.001; odds ratio = 12.940), and preoperative CEA (p = 0.026; odds ratio = 4.124). mrEMVI score 4 was more likely for synchronous metastasis (p = 0.044; odds ratio = 9.429) than mrEMVI score 3 in rectal cancer. Conclusions: mrEMVI positivity is an independent risk factor for synchronous distant metastasis in rectal cancer. mrEMVI score 4 is a stronger risk factor for synchronous metastasis than mrEMVI score 3 in rectal cancer.