• Participants must have diagnosis of hepatocellular carcinoma (HCC) that is deemed unsuitable for surgical resection, transplant, or radiofrequency ablation (RFA). Participants may have up to 5 lesions with a total maximal tumor dimension of \< 20 cm, and no one lesion \> 15 cm. Diagnosis may be confirmed by at least 1 criteria listed below:

‣ Histologically or cytologically proven diagnosis of HCC within 180 days prior to study registration.

⁃ At least 1 solid liver lesion or vascular tumor thrombus (involving portal vein, IVC, and/or hepatic vein) \> 1 cm with arterial enhancement and delayed washout on multiphasic CT or MRI. Radiologic imaging evaluation must occur within 28 days prior to study registration.

⁃ Enhancing vascular thrombosis demonstrating arterial enhancement and delayed washout of multiphasic MRI. Radiologic imaging evaluation must occur within 30 days prior to study registration.

• Participants must have measurable disease, defined as at least one lesion that can be accurately measured in at least one dimension (longest diameter to be recorded for non-nodal lesions and short axis for nodal lesions) as ≥20 mm (≥2 cm) by chest x-ray or as ≥10 mm (≥1 cm) with CT scan, MRI, or calipers by clinical exam. See Section 12 (Measurement of Effect) for the evaluation of measurable disease.

• Small volume extrahepatic disease permitted, defined as \<2.0 cm in sum of maximal diameters (e.g. presence of one 1.8 cm metastatic lymph node, or two 0.8 cm lung lesions are allowed). Bony lesions are included in the \<2.0 cm of extrahepatic disease. Note that benign periportal lymphadenopathy is not unusual in the presence of hepatitis and is permitted, even if the sum of enlarged nodes is \> 2.0 cm. Radiologic imaging of chest, abdomen, and pelvis via CT or MRI is required within 28 days prior to study registration. CT with contrast is required unless contrast is contraindicated.

• Participants may have received transarterial chemoembolization (TACE) or drug eluting beads (DEB). A 2 week (14 day) washout period is required prior to initiating study treatment.

• Age ≥18 years at the time of signing informed consent document.

• ECOG performance status 0-1.

• Child-Pugh A liver function within 7 days of study registration.

• Barcelona Clinic Liver Cancer (BCLC) stages Intermediate (B) or Advanced (C) within 7 days of study registration.

• No evidence of significant portal hypertension.

• Participants must have adequate organ and marrow function as defined the following laboratory results, obtained within 7 days prior to study registration:

‣ absolute neutrophil count ≥1,500/mcL

⁃ absolute lymphocyte count ≥500/mcL

⁃ platelets ≥75,000/mcL without transfusion

⁃ hemoglobin ≥9 g/dL, transfusion allowed to meet this criterion

⁃ total bilirubin ≤ 3 × institutional upper limit of normal (ULN)

⁃ AST(SGOT)/ALT(SGPT) ≤5 × institutional ULN

⁃ alkaline phosphatase(ALP) \<2 × institutional ULN

⁃ creatinine ≤ 1.5 × institutional ULN OR

⁃ estimated creatinine clearance ≥50 mL/min/1.73 m2 (according to the Cockcroft-Gault formula)

⁃ serum albumin ≥2.8 g/dL

⁃ INR or aPTT ≤2 × institutional ULN for participants not receiving therapeutic anticoagulation

⁃ Urine dipstick for proteinuria \<2+; participants discovered to have ≥2+ proteinuria on dipstick urinalysis at baseline should undergo a 24-hour urine collection and must demonstrate \<1g of protein in 24 hours.

• Resolution of any acute, clinically significant treatment-related toxicity from prior therapy to Grade ≤ 1 prior to study entry, with the exception of alopecia.

• No known HIV infection.

• Documented virology status of hepatitis B virus (HBV), as confirmed by screening HBV serology test within 28 days prior to study registration.

‣ For participants with evidence of chronic HBV infection, the HBV viral load must be undetectable on suppressive therapy, if indicated.

⁃ For participants with active HBV, HBV DNA \<500 IU/mL obtained within 28 days prior to initiation of study treatment, and Anti-HBV treatment (per local standard of care; e.g., entecavir) for a minimum of 14 days prior to study entry and willingness to continue treatment for the length of the study.

• Documented virology status of hepatitis C virus (HCV), as confirmed by screening HCV serology test within 28 days prior to study registration.

• Women of childbearing potential (WOCBP) must agree to use appropriate method(s) of contraception to avoid pregnancy during the treatment period and for at least 5 months after the last dose of Atezolizumab or 6 months after the last dose of Bevacizumab. A woman is considered to be of childbearing potential if she is postmenarcheal, has not reached a postmenopausal state (≥ 12 continuous months of amenorrhea with no identified cause other than menopause), and has not undergone surgical sterilization (bilateral tubal ligation, bilateral oophorectomy, or hysterectomy).

• WOCBP must have a negative serum or urine pregnancy test (minimum sensitivity 25 IU/L or equivalent units of HCG) within 14 days prior to study registration.

• Women must not be breastfeeding.

• Men who are sexually active with WOCBP must agree to use any contraceptive method with a failure rate of less than 1% per year during the treatment period and for 6 months after the last dose of Bevacizumab. Men must refrain from donating sperm during this same period.

• Ability to understand and the willingness to sign a written informed consent document