<p>Accurate assessment of aerobic capacity is crucial for athlete monitoring. The 30–15 Intermittent Fitness Test (30–15IFT) provides a practical field-based alternative to laboratory treadmill tests (ITRT), but its validity remains unclear. This systematic review and meta-analysis evaluated the criterion-related validity of 30–15IFT for estimating maximal oxygen uptake (VO₂max), maximal heart rate (HRmax), and maximal running velocity (MRV) compared with ITRT. Following PRISMA guidelines, PubMed, Web of Science, and ScienceDirect were searched up to September 2025. Studies directly comparing 30–15IFT and ITRT were included, and methodological quality was assessed using PEDro and QUADAS-2/C tools. Random-effects meta-analyses estimated pooled biases, limits of agreement (LOA), heterogeneity, and publication bias. Eight studies (<i>n</i> = 158) of moderate quality (PEDro = 3–5) were included. Pooled bias for VO₂max was 1.88&#xa0;ml·kg⁻¹·min⁻¹ (<i>P</i> = 0.15), HRmax bias was 4.35 beats·min⁻¹ (<i>P</i> = 0.054), and MRV bias was 3.08&#xa0;km·h⁻¹ (<i>P</i> &lt; 0.001). Correlations were high for VO₂max (<i>r</i> = 0.69) and HRmax (<i>r</i> = 0.85), and moderate for MRV (<i>r</i> = 0.62). However, relatively wide LOA were observed across all outcomes (VO₂max: -5.28 to 9.04&#xa0;ml·kg⁻¹·min⁻¹; HRmax: −4.97 to + 13.66 beats·min⁻¹; MRV:1.09 to 5.08&#xa0;km·h⁻¹), indicating substantial individual-level variability. Overall, these findings support the use of the 30–15IFT for group-level assessment and monitoring of aerobic and performance-related parameters in athletes. Nevertheless, individual-level interpretation—particularly of absolute VO₂max values—should be approached with caution due to limited agreement with laboratory-based reference measures.</p>