Inclusion Criteria:
- ECOG PS of less than or equal to (<=) 2
- At least 16 weeks of life expectancy at time of entry into the study
- Histologically confirmed colorectal cancer (CRC) with mCRC confirmed radiologically
- Measureable, unresectable disease according to RECIST 1.1
- No prior chemotherapy for CRC in the metastatic setting
- Archival tumor formalin-fixed paraffin-embedded tissue block from the primary tumor obtained at the time of the initial diagnosis is available
- Adequate hematological, liver and renal function
- Agreement to use highly effective measures of contraception
Exclusion Criteria for All Participants:
- Less than 6 months from completion of any prior neoadjuvant or adjuvant chemotherapy, radiotherapy
- Prior or current treatment with bevacizumab or any other anti-angiogenic drug (vascular endothelial growth factor or vascular endothelial growth factor receptor therapies or tyrosine kinase inhibitors)
- Current or recent (within 10 days of study enrollment) use of aspirin (more than [>] 325 milligrams per day [mg/day]), clopidogrel (> 75 mg/day), or current or recent (within 10 days prior to the start of study induction treatment) use of therapeutic oral or parenteral anticoagulants or thrombolytic agents for therapeutic purposes (prophylactic uses allowed)
- Active infection requiring intravenous antibiotics at the start of study induction treatment
- Previous or concurrent malignancy, except for adequately treated basal or squamous cell skin cancer, in situ cervical cancer, or other cancer for which the participant has been disease-free for 5 years prior to study entry
- Inadequately controlled hypertension; prior history of hypertensive crisis or hypertensive encephalopathy
- Clinically significant (active) cardiovascular disease, for example cerebrovascular accidents <= 6 months prior to start of study induction treatment, myocardial infarction <= 6 months prior to study enrollment, unstable angina, New York Heart Association (NYHA) Functional Classification Grade II or greater congestive heart failure, or serious cardiac arrhythmia uncontrolled by medication or potentially interfering with protocol treatment
- Significant vascular disease (e.g., aortic aneurysm requiring surgical repair or recent arterial thrombosis) within 6 months of start of study induction treatment
- Active symptomatic or untreated central nervous system (CNS) metastases; CNS disease other than supratentorial or cerebellar metastases (in other words, patients with metastases to midbrain, pons, medulla or spinal cord are excluded); history of or known carcinomatous meningitis
- Known hypersensitivity to any component of any of the study induction or maintenance treatment medications
- Pregnancy or lactation
Exclusion Criteria for Participants in Cohort 1 (MP):
- Inability to swallow pills
- Refractory nausea and vomiting, malabsorption, external biliary shunt or significant bowel resection that would preclude adequate absorption
- History or presence of clinically significant ventricular or atrial dysrhythmias
- Corrected QT (QTc) interval >= 450 millisecond assessed within 3 weeks prior to randomization, long QT syndrome or, uncorrectable electrolyte abnormalities (including magnesium) or requirement for medicinal products known to prolong the QT interval
- ECOG PS > 2
Exclusion Criteria for Participants in Cohort 2 (MP):
- History of autoimmune disease including but not limited to myasthenia gravis, myositis, autoimmune hepatitis, systemic lupus erythematosus, rheumatoid arthritis, inflammatory bowel disease, vascular thrombosis associated with antiphospholipid syndrome, Wegener's granulomatosis, Sjögren's syndrome, Guillain-Barré syndrome, multiple sclerosis, vasculitis, or glomerulonephritis
- Prior allogeneic bone marrow transplantation or prior solid organ transplantation
- History of idiopathic pulmonary fibrosis (including pneumonitis), drug-induced pneumonitis, organizing pneumonia, or evidence of active pneumonitis at most recent chest imaging (computed tomography [CT] scan or magnetic resonance imaging [MRI])
- Positive test for human immunodeficiency virus (HIV)
- Active hepatitis B virus (HBV) or hepatitis C virus (HCV) at Screening
- Active tuberculosis
- Severe infection within 4 weeks prior to start of maintenance treatment including, but not limited to, hospitalization for complications of infection, bacteremia, or severe pneumonia; has signs or symptoms of significant infection or has received oral or IV antibiotics within 2 weeks prior to start of maintenance treatment
- Administration of a live, attenuated vaccine within 4 weeks prior to start of maintenance treatment or anticipation that such a live attenuated vaccine will be required during the remainder of the study
- Prior treatment with cluster of differentiation (CD) 137 agonists, anti-cytotoxic T-lymphocyte-associated antigen (CTLA) 4, anti-programmed death-1 (PD-1), or anti-programmed death-ligand 1 (PD-L1) therapeutic antibody or pathway-targeting agents
- Treatment with systemic immunostimulatory agents (including but not limited to interferons or interleukin-2) within 4 weeks or five half-lives of the drug, whichever is longer, prior to start of maintenance treatment
- Treatment with systemic corticosteroids or other systemic immunosuppressive medications within 2 weeks prior to start of maintenance treatment, or anticipated requirement for systemic immunosuppressive medications during the remainder of the study
- If receiving receptor activator of nuclear factor kappa-B ligand (RANKL) inhibitor (for example, denosumab) and unwilling to adopt alternative treatment such as bisphosphonates while receiving atezolizumab
Exclusion Criteria for Participants in Cohort 3 (MP):
- Inability to swallow pills
- Left ventricular ejection fraction (LVEF) less than (<) 50 percent (%) as assessed after completion of induction treatment by either 2-dimensional echocardiogram or multiple-gated acquisition
- Clinically significant cardiovascular disease, including unstable angina, history of or active congestive heart failure of ≥ NYHA Grade 2, history of or ongoing serious cardiac arrhythmia requiring treatment (except for controlled atrial fibrillation and/or paroxysmal supraventricular tachycardia).
- Current uncontrolled hypertension with or without medication
- Current dyspnea at rest due to complications of advanced malignancy or other disease requiring continuous oxygen therapy
- Insulin-dependent diabetes
- Current known infection with HIV, HBV, or HCV (active infection or carriers)
- Requirement for concurrent use of the antiviral agent sorivudine (antiviral) or chemically related analogues, such as brivudine
- Malabsorption syndrome, disease significantly affecting gastrointestinal function, resection of the stomach or small bowel, or ulcerative colitis
- Known hypersensitivity to murine proteins
Exclusion Criteria for Participants in Cohort 4 (MP):
- Inability to swallow medications
- History of autoimmune disease including but not limited to myasthenia gravis, myositis, autoimmune hepatitis, systemic lupus erythematosus, rheumatoid arthritis, inflammatory bowel disease, vascular thrombosis associated with antiphospholipid syndrome, Wegener's granulomatosis, Sjögren's syndrome, Guillain-Barré syndrome, multiple sclerosis, vasculitis, or glomerulonephritis
- History of idiopathic pulmonary fibrosis (including pneumonitis), drug-induced pneumonitis, organizing pneumonia (bronchiolitis obliterans, cryptogenic organizing pneumonia), or evidence of active pneumonitis on most recent chest imaging (CT scan or MRI)
- Malabsorption condition that would alter the absorption of orally administered medications
- Amylase or lipase ≥ 1.5 times the upper limit of normal within 14 days prior to maintenance treatment initiation
- Serum albumin less than (<) 2.5 grams per deciliter (g/dL)
- LVEF < institutional lower limit of normal or < 50%, whichever is lower
- Poorly controlled hypertension
- Uncontrolled pleural effusion, pericardial effusion or ascites requiring repeated drainage more than once every 28 days. Indwelling drainage catheters are allowed
- Unstable angina, new onset angina within last 3 months, myocardial infarction within last 6 months and current congestive heart failure ≥ NYHA Grade 2
- History of stroke, reversible ischemic neurological defect, or transient ischemic attack within 6 months prior to initiation of maintenance treatment
- History or evidence of intracranial hemorrhage or spinal cord hemorrhage
- Evidence of clinically significant vasogenic edema
- Any hemorrhage or bleeding event ≥ National Cancer Institute Common Terminology Criteria for Adverse Events Grade 3 within 28 days prior to initiation of maintenance treatment
- History or evidence of retinal pathology on ophthalmologic examination that is considered a risk factor for central serous retinopathy, retinal vein occlusion, or neovascular macular degeneration
- Positive HIV test
- Active HBV or HCV
- Active tuberculosis
- Severe infection within 4 weeks prior to start of maintenance treatment including, but not limited to, hospitalization for complications of infection, bacteremia, or severe pneumonia; has signs or symptoms of significant infection or has received oral or IV antibiotics within 2 weeks prior to start of maintenance treatment.
- Prior allogeneic bone marrow transplantation or prior solid organ transplantation
- Administration of a live, attenuated vaccine within 4 weeks prior to start of study maintenance treatment or anticipation that such a live attenuated vaccine will be required during the study
- Prior treatment with CD137 agonists, anti-CTLA4, anti-PD-1, or anti-PD-L1 therapeutic antibody or pathway-targeting agents
- Prior treatment with a mitogen-activated protein kinase/extracellular signal-regulated kinase (ERK) or ERK inhibitor
- Treatment with systemic immunostimulatory agents (including but not limited to interferons or interleukin-2) within 4 weeks or five half-lives of the drug, whichever is longer, prior to start of study maintenance treatment
- Treatment with systemic corticosteroids or other systemic immunosuppressive medications (including but not limited to prednisone, dexamethasone, cyclophosphamide, azathioprine, methotrexate, thalidomide, and anti-tumor necrosis factor agents) within 2 weeks prior to start of study maintenance treatment, or requirement for systemic immunosuppressive medications during the trial.
- If receiving a RANKL inhibitor (for example, denosumab), unwilling to adopt alternative treatment such as (but not limited to) bisphosphonates, while receiving atezolizumab.
- Consumption of foods, supplements or drugs that are potent cytochrome P450 3A4 (CYP3A4) enzyme inducers or inhibitors ≤ 7 days before initiation of study maintenance treatment or expected concomitant use during maintenance treatment. These include St. John's wort or hyperforin (potent CYP3A4 enzyme inducer) and grapefruit juice (potent CYP3A4 enzyme inhibitor)