<b><i>Introduction:</i></b> The efficacy of systemic first-line treatments in older adults with unresectable hepatocellular carcinoma (HCC) has not been well-studied. We compared the safety and efficacy of atezolizumab plus bevacizumab versus sorafenib as a first-line treatment in younger versus older patients with unresectable HCC. <b><i>Methods:</i></b> This global, phase 3, open-label, randomized clinical trial (IMbrave150) recruited patients aged ≥18 years with locally advanced metastatic or unresectable HCC, an Eastern Cooperative Oncology Group performance status score of 0 or 1, and Child-Pugh class A liver function who had not previously received systemic therapy for liver cancer. Patients received either 1,200 mg atezolizumab plus 15 mg/kg bevacizumab intravenously every 3 weeks or 400 mg sorafenib orally twice daily until loss of clinical benefit or unacceptable toxicity. Primary endpoints were overall survival (OS) and progression-free survival (PFS). Secondary outcomes were the incidence of adverse events and time to deterioration of patient-reported outcomes (PROs). This subgroup analysis evaluated safety and efficacy endpoints in patients &#x3c;65 years, ≥65 to &#x3c;75 years, and ≥75 years. <b><i>Results:</i></b> Of 501 patients, 165 patients were randomized to sorafenib and 336 were randomized to atezolizumab plus bevacizumab (175 patients &#x3c;65 years; 106 patients ≥65 to &#x3c;75 years; 55 patients ≥75 years). Across all age groups, patients receiving atezolizumab plus bevacizumab had longer median OS (&#x3c;65: 18.0 vs. 12.2 months [HR, 0.57; 95% CI: 0.40–0.82]; ≥65 to &#x3c;75: 19.4 vs. 14.9 months [HR, 0.80; 95% CI: 0.52–1.23]; ≥75: 24.0 vs. 18.0 months [HR, 0.72, 95% CI: 0.37–1.41]) and PFS than those receiving sorafenib. Time to deterioration for multiple PROs was delayed for patients receiving atezolizumab plus bevacizumab, including older adults. There were no clinically meaningful differences in toxicity between age groups. <b><i>Conclusion:</i></b> Atezolizumab plus bevacizumab is safe and effective in adults &#x3c;65, ≥65 to &#x3c;75, and ≥75. Treatment was well-tolerated even in elderly patients.