Introduction: Human papillomavirus–vaccinated cohorts, irrespective of age, will likely reduce their subsequent screening requirements, thus opening opportunities for global cost reduction and program sustainability. The determinants of uptake and completion of a 3-dose human papillomavirus vaccination program by adult women in a European context were estimated. Study design: This was an intervention study. Setting/participants: Study participants were women aged 25–45 years, attending opportunistic or population-based cervical cancer screening in Belgium, Denmark, Finland, France, Germany, Slovenia, Spain, Sweden, and the United Kingdom between April 2016 and May 2018. Intervention: Study participants completed a questionnaire on awareness and attitudes on adult female human papillomavirus vaccination and were invited to receive free human papillomavirus vaccination. Main outcome measures: Main outcome measures were acceptance, uptake, and completion of vaccination schedule. Determinants of vaccine uptake were explored using multilevel logistic models in 2019. Results: Among 3,646 participants, 2,748 (range by country=50%–96%) accepted vaccination, and 2,151 (range=30%–93%) received the full vaccination course. The factors associated with higher vaccine acceptance were previous awareness of adult female (OR=1.22, 95% CI=1.00, 1.48) and male (OR=1.59, 95% CI=1.28, 1.97) vaccination. Women in stable relationships (OR=0.56, 95% CI=0.45, 0.69) or with higher educational level (OR=0.76, 95% CI=0.63, 0.93) were more likely to refuse vaccination. Recruitment by postal invitation versus personal invitation from a healthcare professional resulted in lower vaccine acceptance (OR=0.13, 95% CI=0.02, 0.76). Vaccination coverage of >70% of adolescent girls in national public programs was of borderline significance in predicting human papillomavirus vaccine uptake (OR=3.23, 95% CI=0.95, 10.97). The main reasons for vaccine refusal were vaccine safety concerns (range=30%–59%) and the need for more information on human papillomavirus vaccines (range=1%–72%). No safety issues were experienced by vaccinated women. Conclusions: Acceptance and schedule completion were largely dependent on recruitment method, achieved coverage of national vaccination programs, and personal relationship status. Knowledge of benefits and safety reassurance may be critical to expanding vaccination target ages. Study results suggest that there are no major opinion barriers in adult women to human papillomavirus vaccination, especially when vaccination is offered face to face in healthcare settings. Trial Registration: EudraCT Number 2014-003177-42.