A Study to Assess the Safety, Tolerability and Efficacy of ION775

Key Inclusion Criteria: 1. Adult males and females with HTG (fasting TG more than or equal to (≥) 350 milligrams per deciliter (mg/dL) \[3.95 millimoles per liter (mmol/L)\] or with sHTG (fasting TG ≥ 500 mg/dL \[5.65 mmol/L\]). 2. Participants should be on standard of care lipid-lowering medications per local guidelines. Key Exclusion Criteria: 1. Hemoglobin A1c (HbA1c) ≥ 8.5% at Screening. 2. Alanine aminotransferase or aspartate aminotransferase \> 2.0 × upper limit of normal. 3. Total bilirubin \> 1.5 upper limit of normal unless due to Gilbert's syndrome. 4. Estimated GFR \< 30 mL/min/1.73 m\^2. Note: Other protocol pre-specified inclusion/exclusion criteria may apply.