This is a multi-center evaluation of NGM621 in an open-label, single-dose and multiple-dose escalation study in participants with Geographic Atrophy secondary to Age-related Macular Degeneration.

Inclusion Criteria:

1. GA lesion size in the study eye of >=2.5 mm² as assessed by the central reading center
2. BCVA - 54 to 4 letters (20/80 to 20/400 Snellen equivalent) using the standard ETDRS (Early Treatment of Diabetic Retinopathy Study) in the study eye at the Screening and Baseline visits; the fellow eye must have a BCVA of at least 69 letters (Snellen equivalent 20/40) at the Screening and Baseline visits

Exclusion Criteria:

1. GA in either eye because of cause other than AMD
2. History or evidence of glaucoma or ocular hypertension in either eye as defined by investigator
3. Visual impairment in the study eye due to causes other than GA
4. Spherical equivalent of the refractive error in the study eye demonstrating more than -6 Diopters of myopia (prior to cataract or refractive surgery)

Other protocol-defined inclusion/exclusion criteria could apply.