Despite availability of treatments and published guidelines, subjects may have asthma that is inadequately controlled. GlaxoSmithKline is currently developing a once-daily 'closed' triple therapy of an Inhaled Corticosteroids/Long-Acting Beta-2-Agonists/Long-Acting Muscarinic Antagonist (ICS/LAMA/LABA) combination (Fluticasone Furoate/Umeclidinium Bromide/Vilanterol Trifenatate [FF/UMEC/VI]) in a single device, with the aim of providing a new treatment option for the management of asthma by improving lung function, health-related quality of life (HRQoL) and symptom control over established combination therapies. This study has 3 study periods: Run-in, Treatment period and a Follow-up period. Eligible subjects who meet the pre-defined criteria at screening (Visit 1) will enter into a 2-week run-in period. Subjects will continue their pre-screening inhaled medications for asthma (ICS+LABA or ICS+LABA+LAMA) without any change in regimen/dosage until day before Visit 2. At Visit 2 subjects will be allocated to either FF/UMEC/VI 100/62.5/25 or FF/UMEC/VI 200/62.5/25 micrograms (mcg) treatment depending on the asthma control status for 52 weeks. Switching medication from FF/UMEC/VI 100/62.5/25 to FF/UMEC/VI 200/62.5/25 will be permitted in accordance with the control status of the subject assessed by Asthma Control Questionnaire (ACQ)-7 at Week 24 of the treatment period. A follow-up visit will be conducted for approximately 1 week. Subjects will be provided with salbutamol as a rescue medication throughout the study.