A Study to Evaluate Efficacy, Safety and Tolerability in Antiretroviral Therapy (ART)-Experienced Participants of at Least 50 Years of Age Living With Human Immunodeficiency Virus (HIV) With Virologic Suppression Who Switch to DTG/3TC FDC From BIC/FTC/TAF (EYEWITNESS)

Inclusion Criteria: Participants living with HIV-1 with documented plasma HIV-1 RNA <50 c/mL within 3 months prior to Screening. Participants must have been on uninterrupted antiretroviral therapy (ART) for ≥1 year (except for brief periods [less than 30 days] where all ART was stopped due to tolerability and/or safety concerns). Participants must be on uninterrupted BIC/FTC/TAF for at least 6 months prior to Screening. Participants with plasma HIV-1 RNA <50 c/mL at Screening. Participants with no known prior regimen switches due to documented virologic failure (defined as a confirmed plasma HIV 1 RNA ≥200 c/mL). Participants with unknown full treatment/clinical history beyond 5 years prior to Screening may be eligible upon discussion and agreement with the medical monitor. Exclusion Criteria: Women participants who are pregnant or breastfeeding or plan to become pregnant or breastfeed during the study. Participants with any evidence of an active Centers for Disease Control and Prevention (CDC) Stage 3 disease, EXCEPT cutaneous Kaposi's sarcoma not requiring systemic therapy. Historical or current CD4 cell counts less than 200 cells/cubic millimetre (mm^3) are not exclusionary. Participants with signs and symptoms which, in the opinion of the Investigator, are suggestive of active severe acute respiratory syndrome-related coronavirus (SARS-CoV-2) infection within 14 days prior to enrolment. Participants with severe hepatic impairment (Class C) as determined by Child-Pugh classification. Evidence of hepatitis B virus (HBV) infection based on the results of testing at Screening for hepatitis B surface antigen (HBsAg), hepatitis B core antibody (anti-HBc), hepatitis B surface antibody (anti-HBs) and HBV deoxyribonucleic acid (DNA) as follows: Participants positive for HBsAg are excluded; Participants negative for anti-HBs but positive for anti-HBc (negative HBsAg status), whether negative or positive for HBV DNA, are excluded; Participants positive for anti-HBc (negative HBsAg status) and positive for anti-HBs (past and/or current evidence) are immune to HBV and are not excluded. Participants with unstable liver disease (as defined by any of the following: presence of ascites, encephalopathy, coagulopathy, hypoalbuminemia, esophageal or gastric varices, or persistent jaundice or cirrhosis), known biliary abnormalities (with the exception of Gilbert's syndrome or asymptomatic gallstones or otherwise stable chronic liver disease per investigator assessment). Participants with history of liver cirrhosis with or without hepatitis viral co-infection. Participants with untreated syphilis infection (positive rapid plasma reagin [RPR] at Screening without clear documentation of treatment). Participants who are at least 7 days post completed treatment are eligible. Participants with history or presence of allergy or intolerance to the study treatment or their components or drugs of their class or a history of drug or other allergy that, in the opinion of the investigator or Medical Monitor, contraindicates their participation. Ongoing malignancy other than cutaneous Kaposi's sarcoma, basal cell carcinoma, or resected, non-invasive cutaneous squamous cell carcinoma, or cervical, anal or penile intraepithelial neoplasia. Participants who in the investigator's judgment, poses a significant suicidality risk. Participant's history of suicidal behavior and/or suicidal ideation should be considered when evaluating for suicide risk. Participants with any evidence of any major 3TC resistance associated mutations (M184V/I and/or K65R and/or MDR) or presence of any major Integrase strand transfer inhibitor (INSTI) resistance associated mutation in any available prior resistance genotype assay test result. All available historical resistance reports with HIV-1 reverse transcriptase or integrase genotypic data must be provided to ViiV after screening and before enrollment for review by ViiV Virology. Participants with any verified Grade 4 laboratory abnormality with the exception of Grade 4 lipid abnormalities. Alanine aminotransferase (ALT) ≥5 times the upper limit of normal (ULN) or ALT ≥3xULN and bilirubin ≥1.5xULN (with greater than [>]35 percentage [%] direct bilirubin). Participant has estimated creatine clearance <30 millilitres per minute (mL/min) per 1.73 square meter (m^2) using the refitted, race-neutral Chronic Kidney Disease Epidemiology Collaboration (CKD-EPIcr_R) method.