In this study, researchers will learn more about a study drug called litifilimab (BIIB059) in participants with systemic lupus erythematosus (SLE). The study will focus on participants who have active disease and are already taking standard of care medications. These may include antimalarials, steroids, and immunosuppressants. The main objective of the study is to learn about the effect litifilimab has on lowering the activity of the disease. The main question researchers want to answer is: \- How many participants have an improvement in their symptoms after 52 weeks of treatment? Researchers will answer this and other questions by measuring the symptoms of SLE over time using a variety of scoring tools. These include the SLE Responder Index (SRI), the Systemic Lupus Erythematosus Disease Activity Index-2000 (SLEDAI-2K), and the Patient Global Assessment - Visual Analog Scale (PGA-VAS). Researchers will also learn more about the safety of litifilimab. They will study how participants' immune systems respond to litifilimab. Additionally, they will measure the effect litifilimab and SLE have on the quality of life of participants using a group of questionnaires. The study will be done as follows: * After screening, participants will be randomized to receive either a high or low dose of litifilimab, or placebo. A placebo looks like the study drug but contains no real medicine. * All participants will receive either litifilimab or placebo as injections under the skin once every 4 weeks. The treatment period will last 52 weeks. Participants will continue to take their standard of care medications. * Neither the researchers nor the participants will know if the participants are receiving litifilimab or placebo. * There will be a follow-up safety period that lasts up to 24 weeks. * In total, participants will have up to 22 study visits. The total study duration for participants will be up to 80 weeks.