For patients with comorbid cataract and primary open-angle glaucoma (POAG), guidance is lacking as to whether cataract extraction and traditional filtering surgery should be performed as a staged or combined procedure. Achieving this guidance requires an evidence-based understanding of the effects of phacoemulsification alone on intraocular pressure (IOP) in patients with POAG. For this reason, a systematic review and meta-analysis were undertaken to synthesise evidence quantifying the effect of phacoemulsification on IOP and the required number of topical glaucoma medications in patients with cataract and POAG. The authors’ search strategy identified 1613 references, including 453 from MEDLINE, 486 from EMBASE, 112 from CINAHL, 77 from Cochrane Library, 378 from ISI Web of Science, and 107 from BIOSIS databases. After screening for and removing duplicate references, 957 remained. After level 1 screening, 893 articles were excluded leaving 64 potentially relevant references. During level 2 screening, seven references were excluded because of an inadequate follow-up period, two were excluded due to inadequate sample size and 23 were excluded due to inadequate outcome reporting. The remaining 32 records were included for qualitative and quantitative synthesis. A systematic review and meta-analysis was undertaken to analyse all available data on the effects of phacoemulsification and intraocular lens (IOL) implantation as a solo procedure on postoperative IOP and IOP-lowering medication use in patients with POAG. Main outcome measures reported were changes in IOP and changes in postoperative anti-glaucoma medication use. Thirty-two studies (1826 patients) were included in qualitative and quantitative synthesis. Study design, population, location, sample size, preoperative and postoperative IOP measurements, preoperative and postoperative medication use, follow-up period, and methodological quality of each included study were summarised. A 12%, 14%, 15% and 9% reduction in IOP from baseline occurred six, 12, 24, and 36 months after phacoemulsification. A mean reduction of 0.57, 0.47, 0.38, and 0.16 medications per patient of glaucoma medication occurred six, 12, 24, and 36 months after phacoemulsification. Phacoemulsification as a solo procedure does lower IOP in patients with POAG, and reduces dependency on topical glaucoma medications. These effects appear to last at least 36 months with gradual loss of the initial effect noted after two years. Certain populations appear to experience much greater reductions in IOP than others and future work to identify these high responding patients is needed. This systematic review and meta-analysis is the first to consolidate the effects of phacoemulsification on IOP and medication use in patients with POAG at three years after lens extraction.