diff --git a/scripts/firedrake-run-split-tests b/scripts/firedrake-run-split-tests
index 9164168e07..752d2efabe 100755
--- a/scripts/firedrake-run-split-tests
+++ b/scripts/firedrake-run-split-tests
@@ -14,6 +14,14 @@ Usage:
     * <njobs> is the number of different jobs
     * <pytest_args...> are additional arguments that are passed to pytest
 
+  The following environment variables can be used to configure the
+  outer process-tree timeout for each split job:
+
+    * FIREDRAKE_RUN_SPLIT_TESTS_TIMEOUT: maximum wall time for each job
+      (default: 1800s)
+    * FIREDRAKE_RUN_SPLIT_TESTS_KILL_AFTER: grace period before forcibly
+      killing a timed-out job (default: 60s)
+
 Example:
 
     firedrake-run-split-tests 3 4 tests/unit --verbose
@@ -28,7 +36,8 @@ Requires:
   * pytest
   * pytest-split
   * mpi-pytest
-  * GNU parallel"
+  * GNU parallel
+  * GNU timeout"
 
 # Print out help message with no arguments or "-h" or "--help"
 if [[ "$#" -eq "0" ]] || [[ "$1" == "-h" ]] || [[ "$1" == "--help" ]]; then
@@ -39,6 +48,13 @@ fi
 num_procs=$1
 num_jobs=$2
 extra_args=${@:3}
+job_timeout=${FIREDRAKE_RUN_SPLIT_TESTS_TIMEOUT:-1800s}
+kill_after=${FIREDRAKE_RUN_SPLIT_TESTS_KILL_AFTER:-60s}
+
+if ! command -v timeout >/dev/null 2>&1; then
+    echo "GNU timeout is required" >&2
+    exit 1
+fi
 
 if [ $num_procs = 1 ]; then
     # Cannot use mpiexec -n 1 because this can sometimes hang with
@@ -58,10 +74,11 @@ set -x
 
 # This incantation:
 # * Runs pytest under GNU parallel using the right number of jobs
+# * Applies an outer timeout to the whole pytest/mpiexec process tree
 # * Uses tee to pipe stdout+stderr to both stdout and a log file
 # * Writes pytest's exit code to a file called jobN.errcode (for later inspection)
 parallel --line-buffer --tag \
-    "${pytest_cmd} 2>&1 | tee ${log_file_prefix}{#}.log; \
+    "timeout --kill-after=${kill_after} ${job_timeout} ${pytest_cmd} 2>&1 | tee ${log_file_prefix}{#}.log; \
     echo \${PIPESTATUS[0]} > job{#}.errcode" \
     ::: $(seq ${num_jobs})