Purpose: To evaluate the 3-year effectiveness and safety of the XEN63 Gel Stent, both as a standalone procedure and combined with phacoemulsification, in patients with primary open-angle glaucoma (POAG). Methods: This prospective, multicenter, non-randomized study included 85 eyes (85 patients) with medically-uncontrolled POAG. Subjects underwent either XEN63-standalone implantation (n = 46) or combined XEN63 + Phacoemulsification (n = 39). The primary endpoint was the cumulative probability of complete success (IOP ≥ 6 and ≥18 mmHg and reduction in IOP ≥ 20% from baseline without ocular-hypotensive medications) at 36 months. Results: At 36-months, the overall surgical success rate was 67.1% (95% CI: 50.8–86.9%), with significant differences between the standalone (78.3%) and combined groups (53.9%; p = 0.0173). Complete success was achieved in 45.9% of the total cohort. Preoperative mean IOP decreased significantly from 21.3 ± 4.7 mmHg to 14.3 ± 4.3 mmHg at the last-follow-up visit (LFUV) (p < 0.0001). Correspondingly, the mean number of medications was significantly reduced from 2.3 ± 0.8 to 0.7 ± 1.0 (p < 0.0001). Multivariable analysis showed that surgical strategy did not significantly influence IOP reduction. Numerical hypotony (IOP < 6 mmHg) occurred in 23.5% of eyes at Day 1 but resolved in 95% of cases by Month 1. One case of hypotonic maculopathy required device explantation. Serious late-onset events included one endophthalmitis (Month 30) and one retinal detachment (Month 26). Secondary needling was required in 8.2% of eyes. Conclusions: The XEN63 Gel Stent provided sustained IOP reduction and a significantly decreased medication burden over 36 months. Outcomes remained consistent regardless of whether the stent was implanted as a standalone procedure or combined with cataract surgery.