• Participant must have a previous diagnosis of RRMS in accordance with the 2017 revised McDonald criteria.

• Participant must have a current diagnosis of SPMS in accordance with the clinical course criteria revised in 2013 endorsed by an Adjudication Committee.

• Participant must have documented evidence of disability progression observed during the 12 months before screening. Eligibility will be analyzed by an Adjudication Committee.

• Absence of clinical relapses for at least 24 months.

• The participant must have an EDSS score at screening from 3.0 to 6.5 points, inclusive.

• Contraceptive use by men and women should be consistent with local regulations regarding the methods of contraception for those participating in clinical studies.

• For patients eligible to be treated with siponimod: 1) does not tolerate it due to side effects or safety reasons, or 2) has failed siponimod treatment due to perceived lack of efficacy, or 3) has declined siponimod treatment.