Inclusion Criteria:  Age ≥18 years Histologically documented, locally advanced (T4b, any N; or any T, N 2-3) or metastatic urothelial carcinoma (M1, Stage IV) Measurable disease as defined by RECIST v1.1 No prior systemic therapy in the inoperable, locally advanced, or metastatic setting including chemotherapy, immune checkpoint inhibitor therapy, targeted therapy, or investigational agents Archival tumor tissue must be available or a fresh biopsy must be obtained, unless approved by the Medical Monitor Eastern Cooperative Oncology Group (ECOG) performance status of 0-2 Adequate organ function as demonstrated by normal laboratory values  Exclusion Criteria:  Prior treatment with IL-2, IFN-α, or an anti-PD-1, anti-PD-L1, anti-PD-L2, anti-CD137 or CD137 agonists, or cytotoxic T-lymphocyte associated protein 4 (CTLA-4) antibody (including ipilimumab), or any other therapeutic antibody or drug specifically targeting T cell co-stimulation or immune checkpoint pathways in any setting Malignancies other than urothelial carcinoma within 3 years prior to randomization, except for adequately treated basal cell or squamous cell skin cancer, or carcinoma in situ of the breast or of the cervix, or low-grade (Gleason ≤6) prostate cancer on surveillance without any plans for treatment intervention (e.g., surgery, radiation, or castration) Presence of central nervous system (CNS) metastases/leptomeningeal disease requiring immediate treatment with radiation therapy or steroids. QTcF interval > 480 msec. For patients with ventricular pacemakers, QTcF > 500 msec Known hypersensitivity or allergy to avelumab, gemcitabine, cisplatin or carboplatin Known severe hypersensitivity reactions to monoclonal antibodies (Grade ≥3), any history of anaphylaxis, or uncontrolled asthma Prior hematopoietic stem cell or bone marrow transplantation, or solid organ transplantation Pregnant or lactating women Active autoimmune disease that might deteriorate when receiving an immunostimulatory agent  Current use of immunosuppressive medication, EXCEPT for the following:  Intranasal, inhaled, topical steroids, or local steroid injection (e.g., intra-articular injection) Systemic corticosteroids at physiological doses ≤10 mg/day of prednisone or equivalent Steroids as premedication for hypersensitivity reactions (e.g., CT scan premedication)