: To assess the available clinical and economic evidence of erenumab vs onabotulinumtoxinA for chronic migraine (CM) and present de-novo indirect treatment comparisons (ITCs) based on available clinical trial data.: We conducted ITCs based on results from the pivotal 295 trial (NCT02066415) of erenumab vs placebo and published aggregate data from the PREEMPT 1 (NCT00156910) and PREEMPT 2 (NCT00168428) trials of onabotulinumtoxinA vs placebo. ITCs were conducted for CM patients with and without prior administration of onabotulinumtoxinA and among CM patients with ≥3 prior preventive treatment failures. Efficacy was assessed based on responder rates of ≥50% reductions in monthly headache days (MHDs) and monthly migraine days (MMDs) as well as change from baseline in both MHDs and MMDs.: Among patients with CM, 140 mg erenumab was associated with a reduction of 1.2 MHD (p = 0.092) and a reduction of 1.0 MMD (p = 0.174) compared to onabotulinumtoxinA at Week 12. Among onabotulinumtoxinA-naïve patients, erenumab was associated with a reduction of 1.8 MHD (p = 0.026) and 1.4 MMD (p = 0.080) at Week 12. Among patients that had received ≥3 prior preventive treatments, the odds ratios comparing erenumab vs onabotulinumtoxinA were 1.7 for ≥50% responder rates based on reductions in MHD (p = 0.155) and 1.7 for ≥50% responder rates based on reductions in MMD (p = 0.140). These findings suggest directional benefits (although not reaching the threshold of statistical significance) associated with erenumab vs onabotulinumtoxinA for the preventive treatment of CM. Evidence from this study may inform healthcare stakeholders in treatment selection and optimization for patients with CM.