The optimal treatment paradigm for patients with oligometastatic non-small cell lung cancer (NSCLC) remains unclear. Some patients with oligometastatic disease experience prolonged remission after locally consolidative radiation therapy (RT), while others harbor micrometastatic disease (below limits of detection by imaging) and benefit from systemic therapy. To risk-stratify and identify the patients most likely to benefit from locally consolidative RT, we performed a multi-institutional cohort study of 1487 patients with oligometastatic NSCLC undergoing liquid biopsy analysis of circulating tumor DNA (ctDNA). In total, 1880 liquid biopsies were performed and approximately 20% of patients (n = 309) had ctDNA measured prior to RT and after their diagnosis of oligometastatic disease. Patients with undetectable ctDNA (pathogenic or likely pathogenic variants in plasma using the Tempus xF assay) before RT had significantly improved progression-free survival (PFS) (P = 0.004) and overall survival (OS) (P = 0.030). ctDNA maximum variant allele frequency (VAF) pre-RT and ctDNA mutational burden pre-RT were both significantly inversely correlated with PFS (maximum VAF P = 0.008, mutational burden P = 0.003) and OS (maximum VAF P = 0.007, mutational burden P = 0.045). These findings were corroborated by multivariate Cox proportional hazards models that included eight additional clinical and genomic parameters. Overall, these data suggest that in patients with oligometastatic NSCLC, pre-RT ctDNA can potentially identify the patients most likely to benefit from locally consolidative RT and experience prolonged PFS and OS. Similarly, ctDNA may be useful to identify undiagnosed micrometastatic disease where it may be appropriate to prioritize systemic therapies.