Global warming profoundly alters fish life histories, yet its integrated effects on fecundity—particularly cumulative fecundity, which integrates growth‑dependent reproductive output with survival over the reproductive lifespan—remain poorly understood. Here, we develop a temperature‑driven cumulative fecundity model parameterized with growth, mortality and fecundity data from 67 fish species across polar, temperate, subtropical and tropical zones. Using three IPCC emission scenarios (SSP1‑2.6, SSP2‑4.5, SSP5‑8.5), we separately evaluate biomass‑driven effects during the historical period (1950–2014) and temperature‑driven effects during the future period (2015–2050). Applying a theoretical fish model derived from the center of FishBase auximetric plots and consistent with the Temperature‑Size Rule, we find that warming increases the von Bertalanffy growth coefficient K but reduces maximum length by >35% and elevates natural mortality, leading to a net decline in cumulative fecundity. Across climatic zones, temperate and subtropical fishes exhibit a fast‑then‑slow exponential decline, tropical fishes display a rapid exponential decline without subsequent attenuation, while polar fishes show a transient increase in cumulative fecundity within –2 °C to 4 °C, driven by shifts in effective physiological temperature. Historically, biomass depletion drove an exponential decline in cumulative fecundity; under future warming, the decline becomes near‑linear, with greater losses under higher emissions. The North subtropical zone suffers the largest loss, owing to the strongest regional warming and the narrowest thermal safety margin. These findings reveal a “double jeopardy” of historical overfishing and future climate warming on fish reproductive capacity and highlight how warming reshapes fecundity through distinct life-history pathways across thermal regimes. Such differences are likely to influence future recruitment potential and the resilience of marine fish populations under climate change.