Mars' polar layered deposits record its climate history. However, no deposit yet analyzed provides a global water cycle record that can be tied to a specific orbital history. Here, I fill this gap by analyzing H2O ice layer formation in Mars' south polar Massive CO2 Ice Deposit (MCID), a 510,000‐year climate record. Statistical analyses of ∼109 formation model runs compared to observed stratigraphy indicate a variable H2O deposition rate of ∼1, 0.1, and 0.01 mm yr−1 at 20, 24, and 28° ^{\circ}$ obliquity, respectively—likely recording the obliquity‐dependent midlatitude‐to‐pole H2O transport rate. The MCID record allows unprecedented obliquity‐driven H2O ice deposition rate derivation because of its well‐defined age relative to other deposits and its CO2 cold‐trapping effect, which simplifies local seasonal and long‐term H2O flux. The recovery of an orbit‐resolved H2O transport rate is an essential step in elucidating Mars' global, orbit‐driven water cycle. Plain Language Summary Mars' south pole hosts a deposit of alternating CO2 and H2O ice layers, which contain a record of global H2O and CO2 transport as Mars' orbit evolved during the past 510 thousand years. I created a numerical model to simulate the build‐up of the layers over time and ran the model approximately one billion times, each time using a different governing function of H2O ice deposition as a function of Mars' orbital configuration. Using statistical analysis, I found that an H2O ice deposition function that exponentially decreases as a function of obliquity (spin‐axis tilt) best recreates the observed layer sequence. Recovery of a south polar H2O‐ice‐deposition‐versus‐obliquity function is novel and important for elucidating how Mars' global water cycle is driven by its orbital variations. Key Points H2O ice layers in Mars' Massive CO2 Ice Deposit record obliquity‐mediated rates of midlatitude‐to‐pole H2O transport over the past 510 kyr The record's unique CO2 cold‐trapping environment isolates the orbit‐forcing signal from other processes, simplifying its interpretation Orbit‐resolved H2O transport rates place an important new quantitative bound on processes driving Mars' recent (∼3.5 Myr) global water cycle