This systematic meta-analysis is aimed at revealing the physiological, psychological, and neurological mechanisms underpinning paced breathing techniques. A systematic search using keywords related to breathing techniques, and their physiological, neurological, and psychological outcomes was conducted using PROQUEST and PUBMED databases. From 231 abstracts, 32 articles met eligibility criteria and were included in the review with an aggregated sample size of 1,096 participants. This review followed the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) guidelines. Paced breathing was characterized by greater time-domain measures of HRV (SDNN: g = 1.64, p < 0.001; RMSSD: g = 0.93, p = 0.003) than spontaneous breathing. Paced breathing also displayed increases in low-frequency HRV relative to spontaneous breathing (g = 1.19, p < 0.001). However, high-frequency HRV yielded mixed results. Paced breathing was associated with less subjective stress and anxiety scores. Neurological outcomes related to paced breathing found greater global increases in alpha brain waves and the contribution of forebrain and brainstem regions. The analysis revealed the inconsistency surrounding the interpretation of HRV measures and a limited number of studies investigated psychological and neurological effects. Future studies should employ methods that correct for respiration when using frequency-based HRV measures and it is recommended that studies should investigate the effect of paced breathing on brain activity, particularly areas associated with emotion regulation.