<p>Despite the routine use of postmortem lividity (PML) in forensic practice to estimate the postmortem interval, its temporal progression remains inconsistently defined across the literature. This study aimed to synthesize the available evidence on the timing of lividity appearance, complete formation, and fixation, and to evaluate the forensic reliability of these parameters. A systematic review and meta-analysis were conducted following PRISMA guidelines, with protocol registration in PROSPERO. A systematic literature search was conducted across five major databases up to December 2025. Eligible studies included original research on human cadavers assessing external PML in relation to time since death. Data extraction and quality assessment were performed independently by two reviewers. Random-effects meta-analysis using REML estimation was applied to derive pooled estimates for each stage of lividity progression. Eleven studies (<i>n</i> = 1,789) were included qualitatively, with eight studies eligible for quantitative synthesis. The pooled mean times were 3.56&#xa0;h for appearance, 5.80&#xa0;h for complete formation, and 10.33&#xa0;h for fixation. However, extreme heterogeneity was observed across all components (I² = 99.9%), with wide prediction intervals. The observed variability was attributable to inconsistent definitions, heterogeneous assessment methods, and inadequate control of confounding factors. Though a general chronological sequence of PML progression is observed, the substantial heterogeneity limits the reliability of fixed timelines for estimating postmortem interval. The findings highlight substantial uncertainty in traditional textbook timelines and emphasize the need for standardized, objective approaches to enhance the forensic utility of postmortem lividity.</p>