• The participant is at least 18 years of age

• The participant is capable of providing signed informed consent and following with protocol requirements

• The investigator determines active, moderate-to-severe thyroid eye disease (TED) associated with autoimmune thyroid conditions (Graves' disease or Hashimoto's thyroiditis) for the most severely affected eye

• The participant has first onset of active TED symptoms within 12 months before screening

• The participant must have normal thyroid function with the baseline disease under control or have mild hypo or hyperthyroidism at screening. Every effort should be made to correct the mild hypo or hyperthyroidism promptly and to maintain the normal thyroid function for the full duration of the study

• The participant agrees to use birth control consistent with local regulations and the people of child-bearing potential must have a negative blood pregnancy test at screening and a negative urine pregnancy test before receiving the study drug