This study is intended to evaluate the efficacy and safety of ANX005 administered by intravenous (IV) infusion to participants recently diagnosed with Guillain-Barré Syndrome (GBS). The total duration of study participation is approximately 6 months.

Inclusion Criteria:

• Diagnosis of GBS according to the National Institute of Neurological Disorders and Stroke Diagnostic Criteria for Guillain-Barré Syndrome.
• Onset of GBS-related weakness ≤10 days prior to start of infusion.
• GBS-DS score of 3,4, or 5 at screening and at Day 1 prior to infusion.

Exclusion Criteria:

• Clinically significant findings on the screening electrocardiogram (ECG), laboratory test results, or physical examination that are not specific to GBS that may interfere with the conduct of the study, the interpretation of the data, or increase the participant's risk.
• Body weight <30 kilograms (kg) or >150 kg at screening.
• Unresponsive (inexcitable) nerve conduction study results in all nerves tested during screening.
• Previous or intended treatment with either plasma exchange or intravenous immunoglobulin for GBS.
• Diagnosis of a variant of GBS, including Miller Fisher syndrome, Bickerstaff's encephalitis, and overlap syndromes.
• History of prior episode of GBS.
• GBS-related weakness that improved since symptom onset, including an improvement between screening and Day 1 (baseline).