• Time to clinical worsening (TTCW) up to Week 52 [ Time Frame: From baseline to Week 52 ]
  This is the time from randomization to the first clinical worsening event up to Week 52. Clinical worsening is defined as any of the following events: all-cause death, non-planned PH-related hospitalization, increase in World Health Organization Functional Class (WHO FC), deterioration in exercise capacity by at least 15 % from baseline as measured by the 6-minute walk distance or signs/symptoms of right heart failure.
• Longitudinal trend of 6-minute walk distance (6MWD) up to Week 52 [ Time Frame: From baseline to week 52 ]
  The distance walked during the 6-minute walk test (6MWT) will be measured at different timepoints up to Week 52 for each participant.
• Percentage of participants with oxygen desaturation post 6-minute walk test (6MWT) up to week 52 [ Time Frame: From baseine to Week 52 ]
  Oxygen desaturation is defined as a decrease in post-6MWT oxygen saturation (SpO2) by at least 5% from the respective pre-6MWT SpO2 value.
• Percentage of participants with improvement, no change or worsening versus baseline in WHO FC up to Week 52 [ Time Frame: From baseline to Week 52 ]
  The following WHO FC classes are defined: Class I: no limitation of usual physical activity (PA); Class II: mild limitation of PA; Class III: marked limitation of PA; Class IV: unable to perform any PA without symptoms, Dyspnea and/or fatigue may be present at rest and symptoms are increased by almost any PA. Change to a lower WHO FC class (for instance from Class III to Class II) corresponds to a WHO FC improvement. Change to a higher WHO FC class (for instance from Class II to Class III) corresponds to a WHO FC worsening.
• Percentage of participants with all-cause death or PH-related hospitalization up to Week 52 [ Time Frame: From baseline to Week 52 ]
  Participants who have experienced at least one unplanned hospitalization related to PH or died from any cause up to Week 52 are reported.
• Rate of all-cause death or PH-related hospitalizations up to Week 52 [ Time Frame: From baseline to week 52 ]
  This rate will be expressed as per 100-participant years, calculated by dividing the total number of all-cause death or hospitalizations related to PH-worsening by the cumulative exposure up to Week 52 of all participants in each intervention group.
• Change from baseline up to Week 52 in SF-12 scores [ Time Frame: From baseline to Week 52 ]
  The SF-12 is a quality of life self-assessment questionnaire including items related to physical and mental/emotional health. Physical and mental scores are summarized.
• Change from baseline up to Week 52 in King's sarcoidosis questionnaire (KSQ) scores [ Time Frame: From baseline to Week 52 ]
  KSQ is a health status questionnaire validated for patients with sarcoidosis. An overall KSQ score is summarized.
• Change from baseline up to Week 39 in PAH-SYMPACT scores [ Time Frame: From baseline to Week 39 ]
  PAH-SYMPACT (Pulmonary Arterial Hypertension-Symptoms and Impact) is a self-rating questionnaire developed by Actelion and validated for patients with PAH to assess PAH-specific symptoms and their physical and cognitive/emotional impact. The symptom scores and the impact scores are summarized.
• Change from baseline up to Week 52 in PGA-S scores [ Time Frame: From baseline to week 52 ]
  PGA (Patient Global Assessment of Severity) is a self-rating scale used to rate the overall severity of the disease with responses from "none" to "very severe".
• Change from baseline up to Week 52 in CGI-S scores [ Time Frame: from baseline to Week 52 ]
  CGI-S (Clinical Global Impression of Severity) is a Clinician-reported outcome (CRO) used by the investigator to rate the severity of the participant's disease on the day of the CRO administration, with responses from "none" to "severe".
• Change from baseline up to Week 52 in CGI-C scores [ Time Frame: from baseline to Week 52 ]
  CGI-C (Clinical Global Impression of Change) is a Clinician-reported outcome (CRO) used by the investigator to rate the change in the participant's disease on the day of the CRO administration compared to baseline (from "very much better" to "very much worse").

• Drug: Selexipag
  Oral tablets containing 200 µg of selexipag. Depending on the iMTD, participants will receive 1 (200 µg) to 8 (1600 µg) tablets at each administration
  Other Name: JNJ-678896049; ACT-293987
• Drug: Placebo
  Oral tablets without active compound. Participants can receive 1 to 8 tablets at each administration.

• Experimental: Selexipag 200 micro gram (μg)
  Study intervention will be up-titrated to allow each participant to reach their individual maximum tolerated dose (iMTD), in the range of 200 μg to1600 μg (ie, 1 to 8 tablets) bid/qd. Dosing frequency will be bid, except for participants with moderate hepatic impairment (Child-Pugh B) or who are concomitantly taking (a) moderate CYP2C8 inhibitor(s), who receive study intervention qd. The dose will be up-titrated by the investigator/delegate in 200 μg bid/qd increments at weekly intervals during scheduled TCs until reaching the iMTD. If the dose regimen is not well tolerated or symptoms cannot be fully managed with symptomatic treatment, the duration of the titration step can be prolonged to 2 weeks. If needed, the dose can be reduced by 200 μg bid/qd.
  Intervention: Drug: Selexipag
• Placebo Comparator: Placebo
  The comparator will be administered similarly to the experimental intervention.
  Intervention: Drug: Placebo

Main Inclusion Criteria:

• Confirmed diagnosis of sarcoidosis as per ATS criteria
• Sarcoidosis-associated precapillary PH, confirmed by RHC (at rest) within 90 days prior to randomization.
• PH severity according to modified WHO FC II-IV at Screening and randomization; participants in WHO FC IV must be in a stable condition and able to perform a 6MWT.
• Either not receiving treatment with PH-specific treatment or oral PH-specific monotherapy (ie, riociguat or PDE5i or ERA); if on oral PH-specific monotherapy then treatment had to be stable (ie, no introduction of new therapies or changes in dose) for at least 90 days prior to both and the RHC qualifying for enrollment and randomization
• Stable sarcoidosis treatment regimen, ie, no new specific anti-inflammatory treatment for sarcoidosis for at least 90 days, and stable dose(s) for at least 30 days prior to both the RHC qualifying for enrollment and randomization
• 6MWD between 50 and 450 m both at Screening and at the time of randomization.
• Forced vital capacity (FVC) >50% of predicted at Screening.
• FEV1/FVC ≥60%, or if FEV1/FVC <60% then FEV1 must be ≥60% of predicted at Screening.
• Women of childbearing potential must have a negative pregnancy test at screening and randomization, must agree to undertake monthly urine pregnancy tests, and to practice an acceptable method of contraception and agree to remain on an acceptable method while receiving study intervention and until 30 days after last dose of study intervention.
• A woman using oral contraceptives must have been using this method for at least 1 month prior to randomization.

Main Exclusion Criteria:

• PH due to left heart disease (PAWP >15 mmHg).
• History of left heart failure (LHF) as assessed by the investigator including cardiomyopathies, and cardiac sarcoidosis, with a left ventricular ejection fraction (LVEF) <40%.
• Treatment with prostacyclin, prostacyclin analogues or IP receptor agonists (ie, selexipag) within 90 days prior to randomization and/or prior to the RHC qualifying for enrollment, except those given at vasodilator testing during RHC.
• SBP <90 mmHg at Screening or at randomization.
• Included on a lung transplant list or planned to be included until Visit 6 / Week 39.
• Change in dose or initiation of new diuretics and/or calcium channel blockers within 1 week prior to RHC qualifying for enrollment.
• Received an investigational intervention or used an invasive investigational medical device within 90 days prior to randomization.
• Any condition for which, in the opinion of the investigator, participation would not be in the best interests of the participant (eg, compromise well-being), or that could prevent, limit, or confound the protocol-specified assessments.
• Any acute or chronic impairment that may influence the ability to comply with study requirements such as to perform RHC, a reliable and reproducible 6MWT (eg, use of walking aids (cane, walker, etc.), or lung function tests.
• Any other criteria as per selexipag Summary of Product Characteristics (SmPC)