A Trial of the Efficacy and Safety of CVL-865 as Adjunctive Therapy in the Treatment of Focal Onset Seizures

* Participants with a diagnosis of epilepsy with focal onset, as defined in the International League Against Epilepsy (ILAE) Classification of Seizures, focal aware (except participants with only focal aware seizures without a motor component), focal impaired awareness, and focal to bilateral tonic-clonic seizures for at least 2 years prior to signing the Informed Consent Form (ICF) * Participants must have history of an average of 4 or more spontaneous and observable focal onset, as defined in the ILAE Classification of Seizures, focal aware (except participants with only focal aware seizures without a motor component), focal impaired awareness, and focal to bilateral tonic-clonic seizures per 28-day period for at least 3 months (84 days) prior to signing the ICF * Participants who have tried and failed at least 2 appropriate Anti- epileptic drugs (AEDs) in the past and also currently taking 1 to 3 permitted AEDs at a stable dose for 4 Weeks prior to the Screening Visit * Participants with a minimum of 8 focal onset, focal aware, focal impaired awareness, or focal to bilateral tonic-clonic seizures during the 8 week baseline period with no 21-day period free of any of these seizure types * Participants must have had magnetic resonance imaging or contrast enhance computed tomography scan of the brain that demonstrated no progressive structural central nervous system abnormality at the time of the diagnosis of epilepsy * Participants must have a body mass index (BMI) of 17.5 to 40.0 kilogram per meter square (kg/m\^2) and a total body weight greater than (\>) 50 kilograms (kg) \[110 pounds (lbs)\] * Women of childbearing potential must agree to use an effective method of contraception from signing of informed consent throughout the duration of the study and for 30 days post last dose * Male must agree to use condom during treatment and until the end of relevant systemic exposure in the male participant for 94 days following the last dose with Investigational Manufacturing Product (IMP)

* Participants with (genetic) idiopathic generalized epilepsies or combined generalized and focal epilepsies, including a history of Lennox-Gastaut Syndrome * Participants with a history of seizures over the past 12 months that occur at such a high frequency they cannot be counted (eg, repetitive seizures, cluster seizures) * Participants with a history of psychogenic non-epileptic seizures within the year prior to signing the ICF * Participants with a history of status epilepticus within 5 years prior to signing the ICF * Participants with a history of neurosurgery for seizures less than 1 year prior to signing the ICF, or radiosurgery less than 2 years prior to signing the ICF * Participants with a current history of significant cardiovascular, pulmonary, gastrointestinal, renal, hepatic, metabolic, hematological, immunological, or neurological (excluding focal onset epilepsy) disease * Participants who test positive for human immunodeficiency virus (HIV), hepatitis B and/or or hepatitis C infection * Participants with a 12-lead ECG demonstrating : QT interval corrected for heart rate using Fridericia's formula \>450 milliseconds (msec) (average of 3 ECGs obtained at the Screening Visit); QRS interval \>120 msec at the Screening Visit assessed by central reader * Participants with abnormal laboratory test results which includes (Aspartate aminotransferase (AST) or Alanine aminotransferase (ALT) elevated to \>2 × Upper limit of normal range (ULN); Total bilirubin greater than or equal to (\>=)1.5 × ULN; Females: Hemoglobin \<11 gram per deciliter (g/dL); Males: hemoglobin \<12 g/dL; White blood cell (WBC) count \<3.0 x 10 power 9 per liter (10\^9/L); Neutrophil count \<2.0 x 10\^9/L; Platelet count \<150 × 10\^9/L * Use of prohibited medications as listed in the protocol in the absence of appropriate washout phase or the likelihood of requiring treatment during the study period with drugs not permitted by the study protocol * Participants taking any drug that is a sensitive P-glycoprotein (P-gp) and Breast cancer resistance protein (BCRP) substrate * Female participants who are breastfeeding and/or who have a positive pregnancy test result prior to receiving IMP * Participants who are known to be allergic or hypersensitive to the IMP or any of its components * Participants who have participated in any clinical trial within 60 days prior to signing the ICF or who have participated in more than 2 clinical trials within the year prior to signing the ICF * Participants with difficulty swallowing * Participants who answer "Yes" on the C-SSRS Suicidal Ideation Item 4 (Active Suicidal Ideation with Some Intent to Act, Without Specific Plan) and whose most recent episode meeting criteria for this C-SSRS Item 4 occurred within the last 6 months, OR Subjects who answer "Yes" on the C-SSRS Suicidal Ideation Item 5 (Active Suicidal Ideation with Specific Plan and Intent) and whose most recent episode meeting criteria for this CSSRS Item 5 occurred within the last 6 months OR Subjects who answer "Yes" on any of the 5 C-SSRS Suicidal Behavior Items (actual attempt, interrupted attempt, aborted attempt, preparatory acts, or behavior) and whose most recent episode meeting criteria for any of these 5 C-SSRS Suicidal Behavior Items occurred in the last 2 years