Cutibacterium avidum is an emerging causative agent of orthopedic device-related infections (ODRIs). There are no guidelines for the antimicrobial treatment of C. avidum ODRI, but oral rifampin is frequently used in combination with a fluoroquinolone following intravenous antibiotics. We describe the in vivo emergence of combined resistance to rifampin and levofloxacin in a C. avidum strain isolated from a patient with early-onset ODRI treated with debridement, antibiotic treatment, and implant retention (DAIR) using rifampin combined with levofloxacin as the oral treatment. Whole-genome sequencing of C. avidum isolates before and after antibiotic exposure confirmed strain identity and identified new mutations in rpoB and gyrA, leading to amino acid substitutions previously reported to be associated with resistance to rifampin (S446P) and fluoroquinolones (S101L), respectively, in other microbial agents, in the posttherapy isolate. Aside from the molecular insights reported here, this study highlights potential limitations of the combination of oral rifampin and levofloxacin in patients undergoing a DAIR procedure for C. avidum ODRI and the potential need to evaluate specific optimal therapy for emerging ODRI pathogens. IMPORTANCE In this study, we report for the first time the in vivo emergence of dual resistance to levofloxacin and rifampin in C. avidum isolated from a patient who received both antibiotics orally in the setting of a salvage debridement and implant retention of an ODRI. Aside from the molecular insights reported here, this study highlights potential limitations of the combination of oral rifampin and levofloxacin in patients undergoing these surgical procedures and the potential need to evaluate specific optimal therapy for emerging ODRI pathogens.