Overactive bladder (OAB) significantly impairs quality of life in the elderly. Although the intradetrusor injection of botulinum toxin type A (BoNT-A) is a treatment option, its effects on older adults remain uncertain. This study aimed to evaluate the efficacy and safety of BoNT-A intradetrusor injections in elderly OAB patients through a systematic review and meta-analysis. A comprehensive literature search was conducted using the PubMed, Embase, Cochrane Library, Scopus, and CINAHL databases from inception to 30 May 2024. The primary outcomes were improvements in daily urinary incontinence (UI) episodes and patient-reported outcomes, while the secondary outcomes focused on potential adverse events. Four randomized controlled trials with 803 participants were included. BoNT-A injections significantly reduced daily UI episodes at 4–6 weeks (mean difference [MD]: −3.82; 95% confidence interval [CI]: −6.29 to −1.35) and at 12 weeks (MD: −2.17; 95% CI: −3.22 to −1.12). However, BoNT-A was associated with an increased risk of elevated post-void residual (Risk Difference [RD]: 0.154; 95% CI: 0.058 to 0.251) and urinary tract infection (RD: 0.111; 95% CI: 0.005 to 0.217), with no significant difference observed in the initiation of catheterization or hematuria. Trial sequential analysis confirmed a sufficient sample size and statistical power. In conclusion, while BoNT-A effectively manages OAB in the elderly, careful post-injection monitoring is warranted due to its potential risks.