diff --git a/system_wrappers/BUILD.gn b/system_wrappers/BUILD.gn
index 2f30a16..7fc29c9 100644
--- a/system_wrappers/BUILD.gn
+++ b/system_wrappers/BUILD.gn
@@ -96,6 +96,7 @@
   deps = [
     "../rtc_base:checks",
     "../rtc_base:logging",
+    "../rtc_base:stringutils",
     "//third_party/abseil-cpp/absl/strings",
   ]
 }
diff --git a/system_wrappers/include/field_trial.h b/system_wrappers/include/field_trial.h
index 1d0cef4..52db33b 100644
--- a/system_wrappers/include/field_trial.h
+++ b/system_wrappers/include/field_trial.h
@@ -16,7 +16,7 @@
 // Field trials allow webrtc clients (such as Chrome) to turn on feature code
 // in binaries out in the field and gather information with that.
 //
-// By default WebRTC provides an implementaion of field trials that can be
+// By default WebRTC provides an implementation of field trials that can be
 // found in system_wrappers/source/field_trial.cc. If clients want to provide
 // a custom version, they will have to:
 //
@@ -45,10 +45,10 @@
 //
 // Notes:
 //   - NOT every feature is a candidate to be controlled by this mechanism as
-//     it may require negotation between involved parties (e.g. SDP).
+//     it may require negotiation between involved parties (e.g. SDP).
 //
 // TODO(andresp): since chrome --force-fieldtrials does not marks the trial
-//     as active it does not gets propaged to renderer process. For now one
+//     as active it does not get propagated to the renderer process. For now one
 //     needs to push a config with start_active:true or run a local finch
 //     server.
 //
@@ -84,6 +84,18 @@
 
 const char* GetFieldTrialString();
 
+#ifndef WEBRTC_EXCLUDE_FIELD_TRIAL_DEFAULT
+// Validates the given field trial string.
+bool FieldTrialsStringIsValid(const char* trials_string);
+
+// Merges two field trial strings.
+//
+// If a key (trial) exists twice with conflicting values (groups), the value
+// in 'second' takes precedence.
+// Shall only be called with valid FieldTrial strings.
+std::string MergeFieldTrialsStrings(const char* first, const char* second);
+#endif  // WEBRTC_EXCLUDE_FIELD_TRIAL_DEFAULT
+
 }  // namespace field_trial
 }  // namespace webrtc
 
diff --git a/system_wrappers/source/field_trial.cc b/system_wrappers/source/field_trial.cc
index 5b8a756..f1dccc9 100644
--- a/system_wrappers/source/field_trial.cc
+++ b/system_wrappers/source/field_trial.cc
@@ -17,6 +17,7 @@
 #include "absl/strings/string_view.h"
 #include "rtc_base/checks.h"
 #include "rtc_base/logging.h"
+#include "rtc_base/string_encode.h"
 
 // Simple field trial implementation, which allows client to
 // specify desired flags in InitFieldTrialsFromString.
@@ -36,7 +37,7 @@
 //
 //  E.g. invalid config:
 //    "WebRTC-experiment1/Enabled"  (note missing / separator at the end).
-bool FieldTrialsStringIsValid(const absl::string_view trials) {
+bool FieldTrialsStringIsValidInternal(const absl::string_view trials) {
   if (trials.empty())
     return true;
 
@@ -69,6 +70,38 @@
 }
 }  // namespace
 
+bool FieldTrialsStringIsValid(const char* trials_string) {
+  return FieldTrialsStringIsValidInternal(trials_string);
+}
+
+void InsertOrReplaceFieldTrialStringsInMap(
+    std::map<std::string, std::string>* fieldtrial_map,
+    const absl::string_view trials_string) {
+  if (FieldTrialsStringIsValidInternal(trials_string)) {
+    std::vector<std::string> tokens;
+    rtc::split(std::string(trials_string), '/', &tokens);
+    // Skip last token which is empty due to trailing '/'.
+    for (size_t idx = 0; idx < tokens.size() - 1; idx += 2) {
+      (*fieldtrial_map)[tokens[idx]] = tokens[idx + 1];
+    }
+  } else {
+    RTC_DCHECK(false) << "Invalid field trials string:" << trials_string;
+  }
+}
+
+std::string MergeFieldTrialsStrings(const char* first, const char* second) {
+  std::map<std::string, std::string> fieldtrial_map;
+  InsertOrReplaceFieldTrialStringsInMap(&fieldtrial_map, first);
+  InsertOrReplaceFieldTrialStringsInMap(&fieldtrial_map, second);
+
+  // Merge into fieldtrial string.
+  std::string merged = "";
+  for (auto const& fieldtrial : fieldtrial_map) {
+    merged += fieldtrial.first + '/' + fieldtrial.second + '/';
+  }
+  return merged;
+}
+
 std::string FindFullName(const std::string& name) {
   if (trials_init_string == NULL)
     return std::string();
@@ -107,7 +140,7 @@
   RTC_LOG(LS_INFO) << "Setting field trial string:" << trials_string;
 #ifndef WEBRTC_EXCLUDE_FIELD_TRIAL_DEFAULT
   if (trials_string) {
-    RTC_DCHECK(FieldTrialsStringIsValid(trials_string))
+    RTC_DCHECK(FieldTrialsStringIsValidInternal(trials_string))
         << "Invalid field trials string:" << trials_string;
   };
 #endif  // WEBRTC_EXCLUDE_FIELD_TRIAL_DEFAULT
diff --git a/system_wrappers/source/field_trial_unittest.cc b/system_wrappers/source/field_trial_unittest.cc
index 67b841d..fdabe1b 100644
--- a/system_wrappers/source/field_trial_unittest.cc
+++ b/system_wrappers/source/field_trial_unittest.cc
@@ -21,10 +21,15 @@
   InitFieldTrialsFromString("");
   InitFieldTrialsFromString("Audio/Enabled/");
   InitFieldTrialsFromString("Audio/Enabled/Video/Disabled/");
+  EXPECT_TRUE(FieldTrialsStringIsValid(""));
+  EXPECT_TRUE(FieldTrialsStringIsValid("Audio/Enabled/"));
+  EXPECT_TRUE(FieldTrialsStringIsValid("Audio/Enabled/Video/Disabled/"));
 
   // Duplicate trials with the same value is fine
   InitFieldTrialsFromString("Audio/Enabled/Audio/Enabled/");
   InitFieldTrialsFromString("Audio/Enabled/B/C/Audio/Enabled/");
+  EXPECT_TRUE(FieldTrialsStringIsValid("Audio/Enabled/Audio/Enabled/"));
+  EXPECT_TRUE(FieldTrialsStringIsValid("Audio/Enabled/B/C/Audio/Enabled/"));
 }
 
 TEST(FieldTrialValidationTest, RejectsBadInputs) {
@@ -40,6 +45,26 @@
   RTC_EXPECT_DEATH(
       InitFieldTrialsFromString("Audio/Enabled/Video/Disabled/garbage"),
       "Invalid field trials string:");
+  EXPECT_FALSE(FieldTrialsStringIsValid("Audio/EnabledVideo/Disabled/"));
+  EXPECT_FALSE(FieldTrialsStringIsValid("Audio/Enabled//Video/Disabled/"));
+  EXPECT_FALSE(FieldTrialsStringIsValid("/Audio/Enabled/Video/Disabled/"));
+  EXPECT_FALSE(FieldTrialsStringIsValid("Audio/Enabled/Video/Disabled"));
+  EXPECT_FALSE(
+      FieldTrialsStringIsValid("Audio/Enabled/Video/Disabled/garbage"));
+
+  // Empty trial or group
+  RTC_EXPECT_DEATH(InitFieldTrialsFromString("Audio//"),
+                   "Invalid field trials string:");
+  RTC_EXPECT_DEATH(InitFieldTrialsFromString("/Enabled/"),
+                   "Invalid field trials string:");
+  RTC_EXPECT_DEATH(InitFieldTrialsFromString("//"),
+                   "Invalid field trials string:");
+  RTC_EXPECT_DEATH(InitFieldTrialsFromString("//Enabled"),
+                   "Invalid field trials string:");
+  EXPECT_FALSE(FieldTrialsStringIsValid("Audio//"));
+  EXPECT_FALSE(FieldTrialsStringIsValid("/Enabled/"));
+  EXPECT_FALSE(FieldTrialsStringIsValid("//"));
+  EXPECT_FALSE(FieldTrialsStringIsValid("//Enabled"));
 
   // Duplicate trials with different values is not fine
   RTC_EXPECT_DEATH(InitFieldTrialsFromString("Audio/Enabled/Audio/Disabled/"),
@@ -47,6 +72,33 @@
   RTC_EXPECT_DEATH(
       InitFieldTrialsFromString("Audio/Enabled/B/C/Audio/Disabled/"),
       "Invalid field trials string:");
+  EXPECT_FALSE(FieldTrialsStringIsValid("Audio/Enabled/Audio/Disabled/"));
+  EXPECT_FALSE(FieldTrialsStringIsValid("Audio/Enabled/B/C/Audio/Disabled/"));
+}
+
+TEST(FieldTrialMergingTest, MergesValidInput) {
+  EXPECT_EQ(MergeFieldTrialsStrings("Video/Enabled/", "Audio/Enabled/"),
+            "Audio/Enabled/Video/Enabled/");
+  EXPECT_EQ(MergeFieldTrialsStrings("Audio/Disabled/Video/Enabled/",
+                                    "Audio/Enabled/"),
+            "Audio/Enabled/Video/Enabled/");
+  EXPECT_EQ(
+      MergeFieldTrialsStrings("Audio/Enabled/Video/Enabled/", "Audio/Enabled/"),
+      "Audio/Enabled/Video/Enabled/");
+  EXPECT_EQ(
+      MergeFieldTrialsStrings("Audio/Enabled/Audio/Enabled/", "Video/Enabled/"),
+      "Audio/Enabled/Video/Enabled/");
+}
+
+TEST(FieldTrialMergingTest, DchecksBadInput) {
+  RTC_EXPECT_DEATH(MergeFieldTrialsStrings("Audio/Enabled/", "garbage"),
+                   "Invalid field trials string:");
+}
+
+TEST(FieldTrialMergingTest, HandlesEmptyInput) {
+  EXPECT_EQ(MergeFieldTrialsStrings("", "Audio/Enabled/"), "Audio/Enabled/");
+  EXPECT_EQ(MergeFieldTrialsStrings("Audio/Enabled/", ""), "Audio/Enabled/");
+  EXPECT_EQ(MergeFieldTrialsStrings("", ""), "");
 }
 #endif  // GTEST_HAS_DEATH_TEST && RTC_DCHECK_IS_ON && !defined(WEBRTC_ANDROID)
         // && !defined(WEBRTC_EXCLUDE_FIELD_TRIAL_DEFAULT)