Inclusion Criteria:
* Participant must be ≥ 18 years of age inclusive, at the time of signing the informed consent
* Histologic diagnosis of melanoma
* Must be considered surgically operable and may present as any of the following groups:
1. Primary melanoma with clinically apparent regional lymph node metastases, confirmed by pathological diagnosis.
2. Clinically detected recurrence of melanoma at regional lymph node basin(s), confirmed by pathological diagnosis.
3. Clinically or histologically detected primary melanoma involving multiple regional nodal groups, confirmed by pathological diagnosis.
4. Clinically detected single site of nodal metastatic melanoma arising from an unknown primary, confirmed by pathological diagnosis.
5. Participants with in transit or satellite metastases with or without lymph node involvement are allowed if they are considered surgically resectable at Screening by the treating surgical oncologist.
6. Participants with distant cutaneous/subcutaneous, soft tissue or nodal metastases with or without regional lymph node involvement are allowed if they are considered potentially surgically resectable and can be biopsied at Screening by the treating surgical oncologist. Elevated LDH is not an exclusion.
* Participants are eligible for this study either at presentation for primary melanoma with concurrent regional nodal and/or in-transit or distant metastasis, or at the time of clinically detected nodal, in transit, or distant recurrence
* Participants must be evaluated by standard-of-care full body imaging studies including positron emission tomography - computed tomography (PET-CT ;preferred; including diagnostic CT component if possible) or CT (if PET-CT cannot be done) as well as magnetic resonance imaging (MRI) of the brain (or CT if MRI cannot be done) as part of the initial clinical work-up at Screening (no more than 4 weeks prior to Cycle 1, Day 1).
* Have measurable disease based on RECIST v1.1, with at least one anatomically distinct lesion. Lesion or lesions must meet all the following baseline criteria:
1. Accessible for electroporation
2. Must be measured in at least one dimension (longest diameter in the plane of measurement is to be recorded)
3. Greater than 3 mm
* Contraceptive use by men or women should be consistent with local regulations regarding the methods of contraception for those participating in clinical studies.
* Male Participants: Male subjects of childbearing potential must be surgically sterile, or must agree to use adequate method of contraception during the study and at least 5 months following the last day of study drug administration. Note: Abstinence is acceptable if this is the usual lifestyle and preferred contraception for the subject
* Female participants: Women of childbearing potential must have negative serum or urine pregnancy test within 72 hours prior to receiving the first study drug administration. If the urine test is positive or cannot be confirmed as negative, a serum pregnancy test will be required. For women of childbearing potential, must be willing to use an adequate method of contraception from 30 days prior to the first study drug administration and 5 months following last day study drug administration (either tavo or nivolumab); acceptable methods include hormonal contraception (oral contraceptives - as long as on stable dose, patch, implant, and injection), intrauterine devices, or double barrier methods (e.g. vaginal diaphragm/vaginal sponge plus condom, or condom plus spermicidal jelly), sexual abstinence or a vasectomized partner. Women may be surgically sterile or at least 1-year post-last menstrual period. Note: Abstinence is acceptable if this is the usual lifestyle and preferred contraception for the subject.
* Capable of giving signed informed consent which includes compliance with the requirements and restrictions listed in the informed consent form (ICF) and in this protocol
Exclusion Criteria:
* Participant has a known additional malignancy that is progressing or requires active treatment. Exceptions include basal cell carcinoma of the skin, squamous cell carcinoma of the skin that has undergone potentially curative therapy or in situ cervical cancer. Also, includes patients who are considered disease-free for at least 3 years from the last definitive treatment for a second malignancy.
* Participants who have Human Immunodeficiency Virus (HIV) (HIV 1/2 antibodies at Screening). HIV testing at screening is not required unless considered clinically indicated by the treating physician.
* Participants who have active Hepatitis B (e.g., HBsAg reactive) or Hepatitis C (e.g., HCV RNA \[qualitative\] is detected at Screening); Note: Participants who have been vaccinated against Hepatitis B and who are positive only for the Hepatitis B surface antibody are permitted to participate in the study. Hepatitis B and C testing at screening is not required unless considered clinically indicated by the treating physician.
* Participant has a diagnosis of immunodeficiency or is receiving systemic steroid therapy or any other form of immunosuppressive therapy within 7 days prior to the first dose of study drug. The use of physiologic doses of corticosteroids may be approved after consultation with the Principal Investigator.
* Participant has a history of (non-infectious) pneumonitis that required steroids or current pneumonitis.
* Participant has a history of interstitial lung disease.
* Participant has an active infection requiring systemic therapy.
* Participant has a history or current evidence of any condition, therapy, or laboratory abnormality that might confound the results of the trial, interfere with the subject's participation for the full duration of the trial, or is not in the best interest of the subject to participate, in the opinion of the treating investigator.
* Participant has not recovered (i.e., \> Grade 1 at Cycle 1, Day 1) from AEs due to a previously administered agent.
* Participant has known psychiatric or substance abuse disorders that would interfere with cooperation with the requirements of the study.
* Participants who are pregnant or breast feeding or expecting to conceive or father children within the projected duration of the trial, starting with the screening visit through 5 months after the last dose of trial treatment.
* Participants with electronic pacemakers or defibrillators
* Participants who have received a live-virus vaccination within 30 days of the first dose of treatment. Seasonal flu vaccines that do not contain live virus are permitted
* Participants who have received transfusion of blood products (including platelets or red blood cells) or administration of colony stimulating factors (including G-CSF, GM-CSF or recombinant erythropoietin) within 4 weeks prior to study Cycle 1, Day 1.
* Previous treatment with anti-PD1 or anti-PDL1 immunotherapy.
* Participation in another clinical study and systemic therapy within 30 days of Cycle 1, Day 1.
* ECOG Performance Status: \>1
* Inadequate organ function as defined per protocol
* Participant has severe hypersensitivity (≥Grade 3) to nivolumab and/or any of its excipients
