Nemiralisib is being developed as an anti-inflammatory drug for the treatment of inflammatory airways disease. This study is designed to assess the dose response, efficacy, safety, and pharmacokinetics of nemiralisib across a range of doses [up to 750 micrograms (µg)] compared with placebo. The study consists of a Screening Period, a 12-Week Treatment Period and a 12-Week Post-Treatment Follow-Up Period. Approximately 1,250 subjects with an acute moderate or severe exacerbation of COPD requiring standard of care (SoC) therapy will be randomized in this double-blind study. Subjects will be randomized to receive different doses of nemiralisib or placebo via ELLIPTA® inhaler. The total duration of study participation is approximately 6 months (170 days). ELLIPTA is the registered trademark of GlaxoSmithKline (GSK) group of companies.