diff --git a/lib/ec2macosinit/instancehistory.go b/lib/ec2macosinit/instancehistory.go
index 8b70f7e..6c084ce 100644
--- a/lib/ec2macosinit/instancehistory.go
+++ b/lib/ec2macosinit/instancehistory.go
@@ -5,6 +5,7 @@ import (
 	"fmt"
 	"os"
 	"path/filepath"
+	"sync"
 	"time"
 )
 
@@ -41,6 +42,58 @@ func (h HistoryError) Error() string {
 	return h.err.Error()
 }
 
+// HistoryRecorder writes module results to the history file incrementally as
+// each module completes. It is safe for concurrent use from multiple goroutines.
+type HistoryRecorder struct {
+	mu              sync.Mutex
+	instanceID      string
+	historyPath     string
+	historyFilename string
+	startTime       time.Time
+	results         []ModuleHistory
+}
+
+// NewHistoryRecorder creates a HistoryRecorder that will persist results to the
+// given instance history path.
+func NewHistoryRecorder(instanceID, historyPath, historyFilename string) *HistoryRecorder {
+	return &HistoryRecorder{
+		instanceID:      instanceID,
+		historyPath:     historyPath,
+		historyFilename: historyFilename,
+		startTime:       time.Now(),
+	}
+}
+
+// Record appends a module result and flushes the full history to disk.
+func (r *HistoryRecorder) Record(m *Module) error {
+	r.mu.Lock()
+	defer r.mu.Unlock()
+
+	r.results = append(r.results, ModuleHistory{
+		Key:     m.generateHistoryKey(),
+		Success: m.Success,
+	})
+
+	return r.flush()
+}
+
+func (r *HistoryRecorder) flush() error {
+	history := History{
+		InstanceID:      r.instanceID,
+		RunTime:         r.startTime,
+		ModuleHistories: r.results,
+		Version:         historyVersion,
+	}
+
+	historyBytes, err := json.Marshal(history)
+	if err != nil {
+		return fmt.Errorf("ec2macosinit: unable to marshal history: %w", err)
+	}
+
+	path := filepath.Join(r.historyPath, r.instanceID, r.historyFilename)
+	return safeWrite(path, historyBytes)
+}
+
 // GetInstanceHistory takes a path to instance history directory and a file name for history files and searches for
 // any files that match. Then, for each file, it calls readHistoryFile() to read the file and add it to the
 // InstanceHistory struct.
diff --git a/lib/ec2macosinit/instancehistory_test.go b/lib/ec2macosinit/instancehistory_test.go
new file mode 100644
index 0000000..3e531a4
--- /dev/null
+++ b/lib/ec2macosinit/instancehistory_test.go
@@ -0,0 +1,170 @@
+package ec2macosinit
+
+import (
+	"encoding/json"
+	"os"
+	"path/filepath"
+	"sync"
+	"testing"
+
+	"github.com/stretchr/testify/assert"
+	"github.com/stretchr/testify/require"
+)
+
+func TestHistoryRecorder_Record(t *testing.T) {
+	dir := t.TempDir()
+	instanceID := "i-abc123"
+	require.NoError(t, os.MkdirAll(filepath.Join(dir, instanceID), 0755))
+
+	recorder := NewHistoryRecorder(instanceID, dir, "history.json")
+
+	m := &Module{
+		Name:          "testmod",
+		Type:          "command",
+		PriorityGroup: 1,
+		RunOnce:       true,
+		Success:       true,
+	}
+
+	err := recorder.Record(m)
+	require.NoError(t, err)
+
+	// Verify the history file was written
+	data, err := os.ReadFile(filepath.Join(dir, instanceID, "history.json"))
+	require.NoError(t, err)
+
+	var h History
+	require.NoError(t, json.Unmarshal(data, &h))
+
+	assert.Equal(t, instanceID, h.InstanceID)
+	assert.Equal(t, historyVersion, h.Version)
+	require.Len(t, h.ModuleHistories, 1)
+	assert.Equal(t, m.generateHistoryKey(), h.ModuleHistories[0].Key)
+	assert.True(t, h.ModuleHistories[0].Success)
+}
+
+func TestHistoryRecorder_RecordMultiple(t *testing.T) {
+	dir := t.TempDir()
+	instanceID := "i-multi456"
+	require.NoError(t, os.MkdirAll(filepath.Join(dir, instanceID), 0755))
+
+	recorder := NewHistoryRecorder(instanceID, dir, "history.json")
+
+	modules := []*Module{
+		{Name: "mod1", Type: "command", PriorityGroup: 1, RunOnce: true, Success: true},
+		{Name: "mod2", Type: "sshkeys", PriorityGroup: 1, RunPerBoot: true, Success: false},
+		{Name: "mod3", Type: "motd", PriorityGroup: 2, RunPerInstance: true, Success: true},
+	}
+
+	for _, m := range modules {
+		require.NoError(t, recorder.Record(m))
+	}
+
+	data, err := os.ReadFile(filepath.Join(dir, instanceID, "history.json"))
+	require.NoError(t, err)
+
+	var h History
+	require.NoError(t, json.Unmarshal(data, &h))
+
+	assert.Equal(t, instanceID, h.InstanceID)
+	require.Len(t, h.ModuleHistories, 3)
+
+	for i, m := range modules {
+		assert.Equal(t, m.generateHistoryKey(), h.ModuleHistories[i].Key)
+		assert.Equal(t, m.Success, h.ModuleHistories[i].Success)
+	}
+}
+
+func TestHistoryRecorder_RecordConcurrent(t *testing.T) {
+	dir := t.TempDir()
+	instanceID := "i-concurrent789"
+	require.NoError(t, os.MkdirAll(filepath.Join(dir, instanceID), 0755))
+
+	recorder := NewHistoryRecorder(instanceID, dir, "history.json")
+
+	modules := make([]*Module, 20)
+	for i := range modules {
+		modules[i] = &Module{
+			Name:          "mod" + string(rune('A'+i)),
+			Type:          "command",
+			PriorityGroup: 1,
+			RunPerBoot:    true,
+			Success:       true,
+		}
+	}
+
+	var wg sync.WaitGroup
+	for _, m := range modules {
+		wg.Add(1)
+		go func(m *Module) {
+			defer wg.Done()
+			assert.NoError(t, recorder.Record(m))
+		}(m)
+	}
+	wg.Wait()
+
+	data, err := os.ReadFile(filepath.Join(dir, instanceID, "history.json"))
+	require.NoError(t, err)
+
+	var h History
+	require.NoError(t, json.Unmarshal(data, &h))
+
+	assert.Equal(t, instanceID, h.InstanceID)
+	assert.Len(t, h.ModuleHistories, 20)
+}
+
+func TestHistoryRecorder_RecordFailedModule(t *testing.T) {
+	dir := t.TempDir()
+	instanceID := "i-fail000"
+	require.NoError(t, os.MkdirAll(filepath.Join(dir, instanceID), 0755))
+
+	recorder := NewHistoryRecorder(instanceID, dir, "history.json")
+
+	m := &Module{
+		Name:          "failing",
+		Type:          "userdata",
+		PriorityGroup: 2,
+		RunPerInstance: true,
+		Success:       false,
+	}
+
+	require.NoError(t, recorder.Record(m))
+
+	data, err := os.ReadFile(filepath.Join(dir, instanceID, "history.json"))
+	require.NoError(t, err)
+
+	var h History
+	require.NoError(t, json.Unmarshal(data, &h))
+
+	require.Len(t, h.ModuleHistories, 1)
+	assert.False(t, h.ModuleHistories[0].Success)
+}
+
+func TestHistoryRecorder_IncrementalPersistence(t *testing.T) {
+	dir := t.TempDir()
+	instanceID := "i-incr111"
+	require.NoError(t, os.MkdirAll(filepath.Join(dir, instanceID), 0755))
+
+	recorder := NewHistoryRecorder(instanceID, dir, "history.json")
+	historyFile := filepath.Join(dir, instanceID, "history.json")
+
+	m1 := &Module{Name: "first", Type: "command", PriorityGroup: 1, RunOnce: true, Success: true}
+	require.NoError(t, recorder.Record(m1))
+
+	// After first record, file should exist with 1 entry
+	data, err := os.ReadFile(historyFile)
+	require.NoError(t, err)
+	var h1 History
+	require.NoError(t, json.Unmarshal(data, &h1))
+	assert.Len(t, h1.ModuleHistories, 1)
+
+	m2 := &Module{Name: "second", Type: "motd", PriorityGroup: 1, RunPerBoot: true, Success: true}
+	require.NoError(t, recorder.Record(m2))
+
+	// After second record, file should have 2 entries
+	data, err = os.ReadFile(historyFile)
+	require.NoError(t, err)
+	var h2 History
+	require.NoError(t, json.Unmarshal(data, &h2))
+	assert.Len(t, h2.ModuleHistories, 2)
+}
diff --git a/run.go b/run.go
index e205594..baa82e5 100644
--- a/run.go
+++ b/run.go
@@ -82,6 +82,9 @@ func run(baseDir string, c *ec2macosinit.InitConfig) {
 	}
 	c.Log.Info("Successfully gathered instance history")
 
+	// Create a history recorder to persist results incrementally
+	recorder := ec2macosinit.NewHistoryRecorder(c.IMDS.InstanceID, c.HistoryPath, c.HistoryFilename)
+
 	// Process each module by priority level
 	var aggregateFatal bool
 	var aggFatalModuleName string
@@ -140,6 +143,10 @@ func run(baseDir string, c *ec2macosinit.InitConfig) {
 					m.Success = true
 					c.Log.Infof("Skipping module [%s] (type: %s, group: %d) due to Run type setting\n", m.Name, m.Type, m.PriorityGroup)
 				}
+				// Record result incrementally so history is persisted even if a later module crashes
+				if err := recorder.Record(m); err != nil {
+					c.Log.Errorf("Error recording history for module [%s]: %s", m.Name, err)
+				}
 				wg.Done()
 			}(&c.ModulesByPriority[i][j], &c.InstanceHistory)
 		}
@@ -151,14 +158,6 @@ func run(baseDir string, c *ec2macosinit.InitConfig) {
 		}
 	}
 
-	// Write history file
-	c.Log.Infof("Writing instance history for instance %s...", c.IMDS.InstanceID)
-	err = c.WriteHistoryFile()
-	if err != nil {
-		c.Log.Fatalf(computeExitCode(c, 73), "Error writing instance history file: %s", err)
-	}
-	c.Log.Info("Successfully wrote instance history")
-
 	// If any module triggered an aggregate fatal, exit 1
 	if aggregateFatal {
 		c.Log.Fatalf(computeExitCode(c, 1), "Exiting after %s due to failure in module [%s] with FatalOnError set", time.Since(startTime).String(), aggFatalModuleName)