Inclusion Criteria:

          -  Participant must have advanced, metastatic RAS wildtype colorectal cancer and must
             have received at least one line of systemic therapy. Both microsatellite (MSI) high
             and stable (MSS) patients are eligible

          -  Participants may have been intolerant of, progressed on, or failed at least one line
             of systemic chemotherapy. Patients who are currently on first line
             Oxaliplatin-containing chemotherapy regimen are allowed on the trial if they have
             remained stable or better ([partial response]PR or [complete response]CR) for at least
             4 months on that line of treatment and are being considered for maintenance therapy as
             standard of care

          -  Histologic or cytologic diagnosis of colorectal cancer

          -  Participant must have an Eastern Cooperative Oncology Group (ECOG) performance status
             of ≤ 1

          -  Absolute neutrophil count ≥ 1,500/µL

          -  Platelets ≥ 100,000/µL

          -  Hemoglobin ≥ 9 g/dL

          -  Serum creatinine ≤ 1.5 x upper limit of normal (ULN) or calculated creatinine
             clearance ≥ 30 mL/min using the Cockcroft-Gault equation

          -  Total bilirubin ≤ 1.5 x ULN (≤ 2.0 in patients with known Gilberts syndrome) OR direct
             bilirubin ≤ 1 x ULN

          -  Aspartate aminotransferase and alanine aminotransferase ≤ 2.5 x ULN unless liver
             metastases are present, in which case they must be ≤ 5 x ULN

          -  Participant must agree to not donate blood during the study or for 90 days after the
             last dose of study treatment

          -  Female participant has a negative urine or serum pregnancy test within 7 days prior to
             taking study treatment if of childbearing potential and agrees to abstain from
             activities that could result in pregnancy from screening through 180 days after the
             last dose of study

          -  Male participant agrees to use an adequate method of contraception starting with the
             first dose of study treatment through 180 days after the last dose of study treatment

          -  Participant must be able to provide written informed consent

        Exclusion Criteria:

          -  Participant must not be simultaneously enrolled in any interventional clinical trial

          -  Prior therapy with poly ADP (adenosine diphosphate) ribose polymerase (PARP)
             inhibitors or with EGFR inhibitors approved for the treatment of colorectal cancer
             (cetuximab or panitumumab)

          -  Patients with a history of interstitial pneumonitis or pulmonary fibrosis, or evidence
             of interstitial pneumonitis or pulmonary fibrosis during screening

          -  Inability to take oral medications

          -  Participant has had radiation therapy encompassing > 20% of the bone marrow within 2
             weeks; or any radiation therapy within 1 week prior to day 1 of protocol therapy

          -  Participant must not have a known hypersensitivity to components or excipients of
             niraparib or panitumumab

          -  Participant must not have a serious, uncontrolled medical disorder, nonmalignant
             systemic disease, or active, uncontrolled infection. Examples include, but are not
             limited to, uncontrolled ventricular arrhythmia, recent (within 90 days) myocardial
             infarction, uncontrolled major seizure disorder, unstable spinal cord compression,
             superior vena cava syndrome, or any psychiatric disorder that prohibits obtaining
             informed consent

          -  Known history of human immunodeficiency virus (HIV) (HIV 1/2 antibodies)

          -  Participant must not have had diagnosis, detection, or treatment of another type of
             cancer ≤ 2 years prior to initiating protocol therapy (except basal or squamous cell
             carcinoma of the skin and cervical cancer that has been definitively treated)

          -  Participant must not have known active, symptomatic brain or leptomeningeal
             metastases.