Inclusion Criteria:

          -  Patients must have a histologically confirmed diagnosis of urothelial carcinoma of the
             urothelial tract/bladder cancer

          -  Patients must have Clinical Laboratory Improvement Act (CLIA) testing and fit one of
             the following groups:

               -  Confirmed presence of a cancer-associated alteration considered pathogenic/likely
                  pathogenic by FM and/or the Genetics Review Panel in one or more of the following
                  genes: BRCA1, BRCA2, ATM, BAP1, MSH2, PALB2, and BRIP1 or in one or more of the
                  DNA-repair genes tested in the FoundationOne FoundationOneCDx (F1CDx) panel
                  including the following genes (Foundation One mutation analysis results and
                  Foundation Liquid results performed prior to enrollment on this study may be
                  accepted for eligibility review): ABL1, ATR, ATRX, BARD1, BRD4, CCND1, CHEK1,
                  CHEK2, DOT1L, FANCC, FANCE, FANCG, FANCL, IKBKE, MEN1, MLH1, MSH2, MSH6, MUTYH,
                  NPM1, PMS2, POLD1, POLE, RAD51, SMARCB1, STK11

                    -  Note: FoundationOneCDx (F1CDx) is a next generation sequencing based in
                       vitro diagnostic device for detection of substitutions, insertion and
                       deletion alterations (indels), and copy number alterations (CNAs) in 324
                       genes and select gene rearrangements, as well as genomic signatures
                       including microsatellite instability (MSI) and tumor mutational burden (TMB)
                       using DNA isolated from formalin-fixed paraffin embedded (FFPE) tumor tissue
                       specimens

               -  Patients with benign or variants of unknown significance as determined by
                  FoundationOne FoundationOneCDx (F1CDx) panel and Genetics Review Panel review
                  will be included to be followed for survival

          -  Patients 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 computed tomography (CT) scan, magnetic resonance
             imaging (MRI), or calipers by clinical exam

          -  Evidence of disease progression as defined by Response Evaluation Criteria in Solid
             Tumors (RECIST) (version 1.1) during treatment or after the most recent dose of
             therapy with at least one platinum-based regimen of chemotherapy and/or an
             immune-checkpoint inhibitor (atezolizumab, pembrolizumab, nivolumab, avelumab or
             durvalumab) (2-week washout from chemotherapy and 4-weeks washout from monoclonal
             antibodies is required)

          -  Age >= 18 years. Because no dosing or adverse event data are currently available on
             the use of olaparib in patients < 18 years of age, children are excluded from this
             study, but will be eligible for future pediatric trials

          -  Eastern Cooperative Oncology Group (ECOG) performance status =< 1 (or Karnofsky >=
             70%)

          -  Leukocytes >= 3,000/mcL

          -  Absolute neutrophil count >= 1,500/mcL

          -  Platelets >= 100,000/mcL

          -  Total bilirubin =< 1.5 x upper limit of normal (ULN) (for subjects with documented
             Gilbert's disease total bilirubin =< 3.0 mg/dL)

          -  Aspartate aminotransferase (AST) (serum glutamic-oxaloacetic transaminase
             [SGOT])/alanine aminotransferase (ALT) (serum glutamate pyruvate transaminase [SGPT])
             =< 2.5 x institutional upper limit of normal (for subjects with liver metastasis
             AST/ALT =< 5 x ULN)

          -  Creatinine clearance >= 50 mL/min/1.73 m^2

          -  Hemoglobin >= 10 g/dL; transfusions are allowed

          -  Prothrombin time (PT)/international normalized ratio (INR) and activated partial
             thromboplastin time (aPTT) within 1.25 x ULN institutional limits, except where a
             lupus anti-coagulant has been confirmed or the patient is on direct oral anticoagulant
             (DOA)

          -  Patients must be able to tolerate oral medications and not have gastrointestinal
             illnesses that would preclude absorption of olaparib

          -  Pre-clinical data indicate that olaparib adversely affects embryofetal survival and
             development. Therefore, women of child-bearing potential and their partners should
             agree to use two (2) highly effective forms of contraception throughout study
             participation and for at least one (1) month after the last dose of olaparib. Male
             study participants should avoid fathering a child or donating sperm during the study
             and for three (3) months after the last dose of olaparib.

               -  Note: Olaparib is a PARP inhibitor with the potential for teratogenic or
                  abortifacient effects. Because there is a potential risk for adverse events in
                  nursing infants secondary to treatment of the mother with olaparib, breastfeeding
                  should be discontinued if the mother is treated with olaparib

          -  Ability to understand and the willingness to sign a written informed consent document
             or patients with impaired decision making capacity (IDMC) if they are represented by a
             legally authorized representative (LAR)

          -  Patients must provide tumor sample for mutation analysis or be willing to undergo
             mandatory screening biopsy

          -  Postmenopausal or evidence of non-childbearing status for women of childbearing
             potential: negative urine or serum pregnancy test within 28 days of study treatment
             and confirmed prior to treatment on day 1. Postmenopausal is defined as:

               -  Amenorrheic for 1 year or more following cessation of exogenous hormonal
                  treatments

               -  Luteinizing hormone (LH) and follicle stimulating hormone (FSH) levels in the
                  post menopausal range for women under 50

               -  Radiation-induced oophorectomy with last menses > 1 year ago

               -  Chemotherapy-induced menopause with > 1 year interval since last menses

               -  Surgical sterilization (bilateral oophorectomy or hysterectomy)

          -  Patients is willing and able to comply with the protocol for the duration of the study
             including undergoing treatment and scheduled visits and examinations

        Exclusion Criteria:

          -  Patients who have had prior treatment with olaparib or any other PARP inhibitor
             (PARPi)

          -  Patients with myelodysplastic syndrome/acute myeloid leukemia; or baseline features
             suggestive of myelodysplastic syndrome or acute myelogenous leukemia on peripheral
             blood smear or bone marrow biopsy, if clinically indicated

          -  Persistent toxicities (>= Common Terminology Criteria for Adverse Events [CTCAE] grade
             2) with the exception of alopecia, caused by previous cancer therapy

          -  Patients who are receiving any other investigational agents. Patients may be on other
             clinical trials or treatment during screening to determine eligibility

          -  Patients with known brain metastases should be excluded from this clinical trial
             because of their poor prognosis and because they often develop progressive neurologic
             dysfunction that would confound the evaluation of neurologic and other adverse events.
             A scan to confirm the absence of brain metastases is not required. Patients with
             spinal cord compression unless considered to have received definitive treatment for
             this and evidence of clinically stable disease for 28 days

          -  History of allergic reactions attributed to compounds of similar chemical or biologic
             composition of olaparib

          -  Patients receiving any medications or substances that are inhibitors or inducers of
             CYP3A are ineligible. A washout period prior to starting olaparib for patients on
             CYP3A inhibitors is 2 weeks; and the required washout period for CYP3A inducers is 5
             weeks for enzalutamide or phenobarbital and 3 weeks for other agents

               -  Because the lists of these agents are constantly changing, it is important to
                  regularly consult a frequently-updated medical reference texts such as the
                  Physicians' Desk Reference. As part of the enrollment/informed consent
                  procedures, the patient will be counseled on the risk of interactions with other
                  agents, and what to do if new medications need to be prescribed or if the patient
                  is considering a new over-the-counter medicine or herbal product

          -  Pregnant women are excluded from this study because olaparib is a PARP inhibitor agent
             with the potential for teratogenic or abortifacient effects

          -  Any chronic or concurrent acute liver disease

          -  History of stroke, transient ischemic attack (TIA), or myocardial infarction, within 6
             months prior to enrollment

          -  Uncontrolled concurrent disease or illness including but not limited to:

               -  Ongoing or active infection

               -  Symptomatic congestive heart failure, unstable angina pectoris, clinically
                  significant cardiac arrhythmia

               -  Unstable or untreated cardiac conditions or ejection fraction of < 50% as
                  determined by echocardiogram (ECHO) or multiple gated acquisition scan (MUGA)

               -  Uncontrolled diabetes mellitus

               -  Psychiatric illness/social situations that would limit compliance with study
                  requirements

          -  Other severe, acute, or chronic medical or psychiatric condition or laboratory
             abnormality that may increase the risk associated with study participation or study
             drug administration or that may interfere with the interpretation of study results
             and, in the judgment of the investigator, would make the patient inappropriate for the
             study

          -  Immunocompromised patients, e.g., patients who are known to be serologically positive
             for human immunodeficiency virus (HIV)

          -  Patients with known active hepatitis (i.e., hepatitis B or C) due to risk of
             transmitting the infection through blood or other body fluids

          -  Other malignancy within the last 5 years except: adequately treated non-melanoma skin
             cancer, curatively treated in situ cancer of the cervix, ductal carcinoma in situ
             (DCIS), stage 1, grade 1 endometrial carcinoma, or other solid tumors including
             lymphomas (without bone marrow involvement) curatively treated with no evidence of
             disease for >= 5 years. Patients with a history of localized triple negative breast
             cancer or localized resected prostate cancer may be eligible, provided they completed
             their adjuvant chemotherapy more than three years prior to registration, and that the
             patient remains free of recurrent or metastatic disease

          -  Resting electrocardiogram (ECG) with corrected QT (QTc) > 470 msec on 2 or more time
             points within a 24 hour period or family history of long QT syndrome

          -  Patients receiving any systemic chemotherapy or radiotherapy (except for palliative
             reasons) within 2 weeks prior to study treatment

          -  Major surgery within 2 weeks of starting study treatment and patients must have
             recovered from any effects of any major surgery

          -  Previous allogenic bone marrow transplant or double umbilical cord blood
             transplantation (dUCBT)