Patients with autoimmune rheumatic diseases have an increased cardiovascular risk driven by chronic systemic inflammation and frequent dyslipidemia. Niacin (nicotinic acid or vitamin B3) is a classic lipid-lowering agent with pleiotropic effects, including anti-inflammatory properties mediated by the G protein-coupled receptor GPR109A. Despite consistent biological rationale, direct clinical evidence on the use of niacin in rheumatic diseases remains scarce. This narrative review synthesizes the available data covering biological mechanisms, observational studies, clinical data, and current gaps in literature. Few studies were found, including observational analyses associating higher dietary niacin intake with lower prevalence of rheumatoid arthritis and better function in osteoarthritis, as well as a small clinical study demonstrating the benefit of topical nicotinamide in cutaneous discoid lupus lesions. To date, no completed clinical trials have evaluated the use of oral niacin for inflammation modulation or cardiovascular prevention in patients with rheumatoid arthritis, systemic lupus erythematosus, or other autoimmune diseases. Future clinical trials are needed to clarify whether niacin could play a relevant role in rheumatology practice.