This study will evaluate the safety and effectiveness of the study drug belcesiran with placebo (an inactive drug treatment) in treating Alpha-1 Antitrypsin Deficiency-Associated Liver Disease AATLD. Belcesiran or placebo will be administered subcutaneously (via a shot) in the thigh or abdomen. About 46 people will take part in this study in about 30 hospitals and clinics worldwide. If deemed eligible, subjects will be randomized (assigned into a group by chance) into 1 of 3 study cohorts (groups). Subjects in Cohorts 1 will be dosed monthly to receive a total of 7 doses. Subjects in Cohort 2 will be dosed monthly to receive a total of 13 doses. Cohort 3 will be dosed monthly for the first 6 months and then quarterly thereafter for a total of 13 doses. Subjects will be given the option for extended treatment in an optional treatment period of an additional 4 to 6 doses of either belcesiran or placebo up to 72 weeks depending on group assignment. Subjects will then enter a follow up period for up to 96 weeks depending on group assignment. Study participation will last up to 192 weeks (3.5 years).