Inclusion Criteria: 

• Signed informed consent must be obtained prior to participation in the study. The subject's', parent's subject's, parent's or legal guardian's signed written informed consent and child's assent, if appropriate, must be obtained before any assessment is performed. Of note, if the subject reaches age of consent (age as per local law) during the study, they will also need to sign the corresponding study Informed Consent Form (ICF) at the next study visit. 
• Male and female subjects ≥ 12 years of age at the time of screening.
• Chronic Spontaneous Urticaria (CSU) diagnosis for ≥ 6 months.
• Diagnosis of CSU refractory to H1-AH at approved doses at the time of randomization, as defined by all of the following: 
  • The presence of itch and hives for ≥ 6 consecutive weeks at any time prior to Visit 1 (Day - 28 to Day -14) despite current use of non-sedating H1-AH;
  • UAS7 score (range 0-42) ≥ 16 and HSS7 (range 0-21) ≥ 8 during the 7 days prior to randomization (Visit 110, Day 1);
  • Subjects must be on H1-AH at only approved doses for treatment of CSU starting at Visit 1 (Day -28 to Day -14).
• Willing and able to complete a daily symptom eDiary for the duration of the study and adhere to the study visit schedules.

Exclusion Criteria: 

• History of hypersensitivity to any of the study drugs or their excipients or to drugs of similar chemical classes (i.e. to murine, chimeric or human antibodies). 
• Subjects having a clearly defined cause of their chronic urticaria, other than CSU. This includes, but is not limited to, the following: symptomatic dermographism (urticaria factitia), cold-, heat-, solar-, pressure-, delayed pressure-, aquagenic-, cholinergic- or contact-urticaria. 
• Diseases, other than chronic urticaria, with urticarial or angioedema symptoms such as urticarial vasculitis, erythema multiforme, cutaneous mastocytosis (urticaria pigmentosa) and hereditary or acquired angioedema (eg, due to C1 inhibitor deficiency). 
• Subjects with evidence of helminthic parasitic infection as evidenced by stools being positive for a pathogenic organism according to local guidelines. All subjects will be screened at Visit 1. If stool testing is positive for pathogenic organism, the subject will not be randomized and will not be allowed to rescreen. 
• Any other skin disease associated with chronic itching that might influence in the investigators opinion the study evaluations and results (e.g. atopic dermatitis, bullous pemphigoid, dermatitis herpetiformis, senile pruritus, etc.).
• Prior exposure to ligelizumab or omalizumab. 
• Any H2 antihistamine, LTRA (montelukast or zafirlukast) or H1 antihistamines use at greater than approved doses after Visit 1.