This is a study to evaluate the clinical efficacy and safety of sonelokimab administered subcutaneously compared with placebo in the treatment of adult participants with moderate to severe hidradenitis suppurativa. Participants will be randomized 2:1 to either sonelokimab or matching placebo up to Week 16.

Inclusion Criteria:

1. Participants must be at least 18 years of age at the time of signing the informed consent.
2. Participants who are diagnosed with hidradenitis suppurativa as determined by the investigator and have a history of signs and symptoms of hidradenitis suppurativa for at least 6 months before signing the informed consent.
3. Participants who have had an inadequate response to appropriate systemic antibiotics for treatment of hidradenitis suppurativa (or demonstrated intolerance to, or had a contraindication to, systemic antibiotics for treatment of their HS), in the investigator's opinion.
4. Participants who have a total AN count of ≥5.
5. Participants who have HS lesions present in ≥2 distinct anatomical areas, at least one of which must contain single or multiple fistulas (ie, be Hurley Stage II or III).

Exclusion Criteria:

1. Participants with a known hypersensitivity to sonelokimab or any of its excipients.
2. Participants with any other active skin disease or condition that may, in the opinion of the investigator, interfere with the assessment of HS.
3. Participants with underlying conditions that, in the opinion of the investigator, potentially places the participant at unacceptable risk.
4. Participants with current severe or uncontrolled disease(s) that put(s) the participant at increased risk in the investigator's opinion, would preclude the participant from adhering to the protocol or completing the study per protocol.
5. Participants with any other known autoimmune disease or any medical condition that in the opinion of the investigator would interfere with an accurate assessment of clinical symptoms of HS.
6. Participants with a gastrointestinal condition including inflammatory bowel disease or diagnosis of ulcerative colitis or Crohn's disease.