To compare the intraocular pressure (IOP)-lowering efficacy and safety of netarsudil once daily (QD) and timolol twice daily (BID). Double-masked, randomized, phase 3, noninferiority study. Patients with open-angle glaucoma or ocular hypertension (unmedicated baseline IOP >20 to <30 mm Hg at 8:00 AM) were randomized to netarsudil ophthalmic solution 0.02% QD (PM) or timolol ophthalmic solution 0.5% BID. The primary endpoint was mean IOP at 8:00 AM, 10:00 AM, and 4:00 PM at week 2, week 6, and month 3 in patients with baseline IOP <25 mm Hg (per-protocol population). Safety was recorded over the 6-month treatment period. A total of 186 patients from each treatment arm were included in the primary efficacy analysis. Netarsudil QD met the criteria for noninferiority to timolol BID. Mean treated IOP ranged from 16.3 to 17.9 mm Hg for netarsudil and 16.7 to 17.6 for timolol, with mean reductions from baseline of 3.9 to 4.7 mm Hg and 3.8 to 5.2 mm Hg, respectively. In prespecified secondary analyses, netarsudil demonstrated noninferiority to timolol in patients with baseline IOP <27 mm Hg and <30 mm Hg. The IOP-lowering effects of netarsudil were sustained over 6 months of treatment. No treatment-related serious adverse event (AE) was reported for either study drug. However, statistically significant reductions in mean heart rate were recorded at all study visits for the timolol group. The most frequent ocular AE among netarsudil-treated patients was conjunctival hyperemia (47.9%), which was predominately mild. Netarsudil QD (PM), a first-in-class IOP-lowering medication, was noninferior to timolol BID and was associated with tolerable ocular AEs.