diff --git a/kits/branch/branch-5/src/main/kotlin/com/mparticle/kits/BranchMetricsKit.kt b/kits/branch/branch-5/src/main/kotlin/com/mparticle/kits/BranchMetricsKit.kt
index 9c863b57f..e5dc61802 100644
--- a/kits/branch/branch-5/src/main/kotlin/com/mparticle/kits/BranchMetricsKit.kt
+++ b/kits/branch/branch-5/src/main/kotlin/com/mparticle/kits/BranchMetricsKit.kt
@@ -49,6 +49,7 @@ class BranchMetricsKit :
     private var isMpidIdentityType = false
     var identityType: IdentityType? = IdentityType.CustomerId
     private var mSendScreenEvents = false
+    private var sendSessionId = false
     private var branchUtil: BranchUtil? = null
 
     override fun getInstance(): Branch? = branch
@@ -74,6 +75,7 @@ class BranchMetricsKit :
         mSendScreenEvents =
             sendScreenEvents != null &&
             sendScreenEvents.equals("true", ignoreCase = true)
+        sendSessionId = settings[SEND_SESSION_ID].equals("true", ignoreCase = true)
         setIdentityType(settings)
         return emptyList()
     }
@@ -120,7 +122,10 @@ class BranchMetricsKit :
     ): List<ReportingMessage> = emptyList()
 
     override fun logEvent(event: MPEvent): List<ReportingMessage> {
-        branchUtil?.createBranchEventFromMPEvent(event)?.logEvent(context)
+        branchUtil
+            ?.createBranchEventFromMPEvent(event)
+            ?.withSessionId(currentSessionId, event.customAttributeStrings)
+            ?.logEvent(context)
         val messages = LinkedList<ReportingMessage>()
         messages.add(ReportingMessage.fromEvent(this, event))
         return messages
@@ -134,7 +139,10 @@ class BranchMetricsKit :
     ): List<ReportingMessage> = emptyList()
 
     override fun logEvent(commerceEvent: CommerceEvent): List<ReportingMessage> {
-        branchUtil?.createBranchEventFromMPCommerceEvent(commerceEvent)?.logEvent(context)
+        branchUtil
+            ?.createBranchEventFromMPCommerceEvent(commerceEvent)
+            ?.withSessionId(currentSessionId, commerceEvent.customAttributeStrings)
+            ?.logEvent(context)
         val messages: MutableList<ReportingMessage> = LinkedList()
         messages.add(ReportingMessage.fromEvent(this, commerceEvent))
         return messages
@@ -151,7 +159,7 @@ class BranchMetricsKit :
                 eventAttributes = HashMap()
             }
             branchUtil?.updateBranchEventWithCustomData(logScreenEvent, eventAttributes)
-            logScreenEvent.logEvent(context)
+            logScreenEvent.withSessionId(currentSessionId, eventAttributes).logEvent(context)
             val messages =
                 LinkedList<ReportingMessage>()
             messages.add(
@@ -168,6 +176,9 @@ class BranchMetricsKit :
         }
     }
 
+    private val currentSessionId: Long?
+        get() = if (sendSessionId) MParticle.getInstance()?.currentSession?.sessionID else null
+
     private val branch: Branch?
         get() = settings[branchAppKey]?.let { Branch.getInstance() }
 
@@ -315,9 +326,25 @@ class BranchMetricsKit :
 
     override fun onApplicationBackground() {}
 
+    /**
+     * Adds the mParticle session ID to the event's custom data. A customer attribute with the same
+     * key wins, and nothing is added without a session ID.
+     */
+    internal fun BranchEvent.withSessionId(
+        sessionId: Long?,
+        attributes: Map<String, String>?,
+    ): BranchEvent =
+        apply {
+            if (sessionId != null && sessionId != 0L && attributes?.containsKey(SESSION_ID_KEY) != true) {
+                addCustomDataProperty(SESSION_ID_KEY, sessionId.toString())
+            }
+        }
+
     companion object {
         private const val FORWARD_SCREEN_VIEWS = "forwardScreenViews"
         private const val USER_IDENTIFICATION_TYPE = "userIdentificationType"
+        private const val SEND_SESSION_ID = "sendSessionId"
+        internal const val SESSION_ID_KEY = "mp_session_id"
         const val NAME = "Branch Metrics"
     }
 }
diff --git a/kits/branch/branch-5/src/test/kotlin/com/mparticle/kits/BranchKitTests.kt b/kits/branch/branch-5/src/test/kotlin/com/mparticle/kits/BranchKitTests.kt
index dc92f808d..68ccf4c9f 100644
--- a/kits/branch/branch-5/src/test/kotlin/com/mparticle/kits/BranchKitTests.kt
+++ b/kits/branch/branch-5/src/test/kotlin/com/mparticle/kits/BranchKitTests.kt
@@ -2,6 +2,7 @@ package com.mparticle.kits
 
 import android.content.Context
 import com.mparticle.MParticleOptions
+import io.branch.referral.util.BranchEvent
 import org.junit.Assert
 import org.junit.Test
 import org.mockito.Mockito
@@ -50,4 +51,59 @@ class BranchKitTests {
         }
         Assert.fail("$className not found as a known integration.")
     }
+
+    /**
+     * Verifies the session ID is added to the Branch event's custom data.
+     */
+    @Test
+    fun testWithSessionIdAddsSessionId() {
+        val branchEvent = Mockito.mock(BranchEvent::class.java)
+
+        with(BranchMetricsKit()) { branchEvent.withSessionId(-7046029254386353131L, mapOf("color" to "blue")) }
+
+        Mockito
+            .verify(branchEvent)
+            .addCustomDataProperty(BranchMetricsKit.SESSION_ID_KEY, "-7046029254386353131")
+    }
+
+    /**
+     * Verifies a customer attribute with the session ID key is not overwritten.
+     */
+    @Test
+    fun testWithSessionIdKeepsCustomerValue() {
+        val branchEvent = Mockito.mock(BranchEvent::class.java)
+
+        with(BranchMetricsKit()) {
+            branchEvent.withSessionId(
+                -7046029254386353131L,
+                mapOf(BranchMetricsKit.SESSION_ID_KEY to "customer-value"),
+            )
+        }
+
+        Mockito.verifyZeroInteractions(branchEvent)
+    }
+
+    /**
+     * Verifies nothing is added when there is no current session.
+     */
+    @Test
+    fun testWithSessionIdSkipsWithoutSession() {
+        val branchEvent = Mockito.mock(BranchEvent::class.java)
+
+        with(BranchMetricsKit()) { branchEvent.withSessionId(null, null) }
+
+        Mockito.verifyZeroInteractions(branchEvent)
+    }
+
+    /**
+     * Verifies nothing is added when the session has no UUID, which the SDK reports as an ID of 0.
+     */
+    @Test
+    fun testWithSessionIdSkipsZeroId() {
+        val branchEvent = Mockito.mock(BranchEvent::class.java)
+
+        with(BranchMetricsKit()) { branchEvent.withSessionId(0L, null) }
+
+        Mockito.verifyZeroInteractions(branchEvent)
+    }
 }