Background: Protection of replication forks is critical for the survival of cancer cells. Chemotherapeutic drugs such as oxaliplatin and irinotecan can impede the progression of replication forks by inducing DNA lesions, which cause fork collapse and generate double-strand breaks. We hypothesized that functional genetic variants in genes involved in the maintenance of replication forks may predict the efficacy of cytotoxic drugs in mCRC patients. Methods: We analyzed genomic and clinical data from MAVERICC, a phase II trial which compared mFOLFOX6 and FOLFIRI in combination with bevacizumab in untreated mCRC patients. Genomic DNA extracted from blood samples was genotyped using an OncoArray (Illumina, Inc., San Diego, CA, USA). Candidate six missense single nucleotide polymorphisms (SNPs) (SLFN11 rs9898983, SLFN11 rs12453150, RPA1 rs5030749, MCM3 rs2230240, TIMELESS rs2291739, and TIMELESS rs774047) were tested for association with progression-free survival (PFS) and overall survival (OS), using Cox proportional hazards model. To confirm the predictive value, the treatment-by-SNP interaction was tested. Results: A total of 324 patients were available for the SNP analyses (mFOLFOX6 plus bevacizumab arm [OHP arm]: n = 161; FOLFIRI plus bevacizumab arm [IRI arm]: n = 163). In the OHP arm, univariable analysis showed a significantly better PFS in patients with G/G genotype of TIMELESS rs2291739 compared to those with any A allele, and in patients with T/T genotype of TIMELESS rs774047 compared to those with any C allele. However, neither of these SNP’s associations were confirmed by multivariable analysis: TIMELESS rs2291739 (any A allele vs G/G, hazard ratio [HR] = 0.60, 95% confidence interval [CI] = 0.31–1.17, p = 0.12) and TIMELESS rs774047 (any C allele vs T/T, HR = 0.74, 95% CI = 0.41–1.36, p = 0.33). In the IRI arm, univariable analysis showed a significantly worse OS in patients with G/G genotype of TIMELESS rs2291739 compared to those with any A allele, and in patients with T/T genotype of TIMELESS rs774047 compared to those with any C allele. Multivariable analysis confirmed the significant associations in these SNPs: TIMELESS rs2291739 (any A allele vs G/G, HR = 3.06, 95% CI = 1.49–6.25, p< 0.01) and TIMELESS rs774047 (any C allele vs T/T, HR = 2.95, 95% CI = 1.43–6.08, p< 0.01). Treatment-by-SNP interaction test confirmed the significant predictive value of both SNPs, both on PFS and OS. Conclusions: Germline polymorphisms in the TIMELESS gene involved in the protection of replication forks may predict efficacy of oxaliplatin and irinotecan in mCRC patients. Our novel findings warrant further validation studies.