Randomized participants aged >=2 years received macitentan orally (dispersible tablet reconstituted in water) once daily based on their body weight (BW): 3.5 milligrams (mg) for BW >=10 kilograms (kg) and <15 kg, 5.0 mg for >=15 kg and <25 kg, 7.5 mg for >=25 kg and <50 kg, and 10.0 mg for >=50 kg. Every 12 weeks body weight was checked for potential dose adjustment. Phosphodiesterase Type 5 inhibitor (PDE-5i) was the only allowed PAH-specific background medication until disease progression. Participants received treatment from Day 1 up to 312.4 weeks.

Randomized participants aged >=2 years continued their SoC as per site's clinical practice which comprised treatment with the pulmonary arterial hypertension (PAH) non-specific treatment and/or up to 2 PAH-specific medications excluding macitentan and intravenous (IV)/subcutaneous (SC) prostanoids. Participants continued to receive the PDE-5i (sildenafil and tadalafil), or other PAH-specific treatment such as an ERA (bosentan and ambrisentan) or oral prostanoids (soluble guanylate cyclase stimulators [riociguat]), which was ongoing at the time of randomization. Additional PAH-specific therapy other than macitentan and IV or SC prostanoids initiated prior to randomization was continued. Participants received treatment from Day 1 up to 316.4 weeks. For participants with disease progression, crossover to macitentan was offered after confirmation of a disease progression event by the blinded Clinical Event Committee.

Enrolled participants aged <2 years received macitentan 2.5 mg once daily orally (dispersible tablet reconstituted in water). Oral or inhaled prostanoid treatment were allowed as PAH-specific background therapy. Participants received treatment from Day 1 up to 72.9 weeks.

Enrolled participants aged >=12 to <18 years received macitentan orally (dispersible tablet reconstituted in water) once daily based on their body weight (BW): 3.5 milligrams (mg) for BW >=10 kilograms (kg) and <15 kg, 5.0 mg for >=15 kg and <25 kg, 7.5 mg for >=25 kg and <50 kg and 10.0 mg for >=50 kg. Every 12 weeks body weight was checked for potential dose adjustment. Phosphodiesterase Type 5 (PDE-5) inhibitor was the only allowed PAH-specific background medication until disease progression. Participants received treatment from Day 1 up to 48.29 weeks.

Total of all reporting groups

Randomized participants aged >=2 years received macitentan orally (dispersible tablet reconstituted in water) once daily based on their body weight (BW): 3.5 milligrams (mg) for BW >=10 kilograms (kg) and <15 kg, 5.0 mg for >=15 kg and <25 kg, 7.5 mg for >=25 kg and <50 kg, and 10.0 mg for >=50 kg. Every 12 weeks body weight was checked for potential dose adjustment. Phosphodiesterase Type 5 inhibitor (PDE-5i) was the only allowed PAH-specific background medication until disease progression. Participants received treatment from Day 1 up to 312.4 weeks.

Enrolled participants aged <2 years received macitentan 2.5 mg once daily orally (dispersible tablet reconstituted in water). Oral or inhaled prostanoid treatment were allowed as PAH-specific background therapy. Participants received treatment from Day 1 up to 72.9 weeks.

Randomized participants aged >=2 years continued their SoC as per site's clinical practice which comprised treatment with the pulmonary arterial hypertension (PAH) non-specific treatment and/or up to 2 PAH-specific medications excluding macitentan and intravenous (IV)/subcutaneous (SC) prostanoids. Participants continued to receive the PDE-5i (sildenafil and tadalafil), or other PAH-specific treatment such as an ERA (bosentan and ambrisentan) or oral prostanoids (soluble guanylate cyclase stimulators [riociguat]), which was ongoing at the time of randomization. Additional PAH-specific therapy other than macitentan and IV or SC prostanoids initiated prior to randomization was continued. Participants received treatment from Day 1 up to 316.4 weeks. For participants with disease progression, crossover to macitentan was offered after confirmation of a disease progression event by the blinded Clinical Event Committee.

Participants aged >=2 years randomized to SoC arm and who had Clinical Event Committee-confirmed disease progression were offered to cross-over to macintentan treatment by signing a separate informed consent, if they agreed per investigator judgment. Eligible participants received macitentan orally (dispersible tablet reconstituted in water) once daily based on their BW: 3.5 mg for BW >=10 kg and <15 kg, 5.0 mg for >=15 kg and <25 kg, 7.5 mg for >=25 kg and <50 kg and 10.0 mg for >=50 kg. Every 12 weeks body weight was checked for potential dose adjustment. Participants received treatment from Day of disease confirmation up to 107 weeks.

Enrolled participants aged >=12 to <18 years received macitentan orally (dispersible tablet reconstituted in water) once daily based on their body weight (BW): 3.5 milligrams (mg) for BW >=10 kilograms (kg) and <15 kg, 5.0 mg for >=15 kg and <25 kg, 7.5 mg for >=25 kg and <50 kg and 10.0 mg for >=50 kg. Every 12 weeks body weight was checked for potential dose adjustment. Phosphodiesterase Type 5 (PDE-5) inhibitor was the only allowed PAH-specific background medication until disease progression. Participants received treatment from Day 1 up to 48.29 weeks.