diff --git a/src/access_moppy/base.py b/src/access_moppy/base.py
index 56843b26..d541df04 100644
--- a/src/access_moppy/base.py
+++ b/src/access_moppy/base.py
@@ -735,6 +735,41 @@ def ordered(ds, core=("lat", "lon", "time", "height")):
 
         self.ds = ordered(self.ds)
 
+    def ensure_time_first(self):
+        """
+        Ensure `time` is the first dimension in all CMORised data variables.
+
+        CMIP tables do not always list `time` first (e.g. `longitude latitude time`),
+        but actual CMIP6 NetCDF files follow the NetCDF convention of placing the
+        unlimited record dimension first: `(time, [vertical], lat, lon)`.
+
+        This method transposes any data variable whose leading dimension is not
+        `time` while preserving the relative order of the remaining dimensions.
+        Coordinate variables (1-D coords, bounds, scalar coords) are left untouched.
+        """
+        if "time" not in self.ds.dims:
+            return
+
+        for var in list(self.ds.variables):
+            dims = list(self.ds[var].dims)
+            if "time" in dims and dims[0] != "time":
+                new_order = ["time"] + [d for d in dims if d != "time"]
+                self.ds[var] = self.ds[var].transpose(*new_order)
+
+        current_sizes = list(self.ds.sizes.keys())
+        if current_sizes and current_sizes[0] == "time":
+            return
+
+        ordered_vars = {}
+        for name in ("time", "time_bnds"):
+            if name in self.ds.variables:
+                ordered_vars[name] = self.ds[name]
+        for name in self.ds.variables:
+            if name not in ordered_vars:
+                ordered_vars[name] = self.ds[name]
+
+        self.ds = xr.Dataset(ordered_vars, attrs=self.ds.attrs)
+
     def _build_drs_path(self, attrs: Dict[str, str]) -> Path:
         """
         Build DRS path using the vocabulary class's controlled vocabulary specifications.
@@ -1259,6 +1294,8 @@ def run(self, write_output: bool = False):
         self.standardize_missing_values()
         self.update_attributes()
         self.reorder()
+        # Ensure time is the leading dimension, matching NetCDF/CMIP6 conventions
+        self.ensure_time_first()
         # Final rechunking before writing for optimal I/O performance
         if write_output:
             self.rechunk_dataset()