diff --git a/src/init.cpp b/src/init.cpp
--- a/src/init.cpp
+++ b/src/init.cpp
@@ -1030,6 +1030,8 @@
     argsman.AddArg("-uacomment=<cmt>",
                    "Append comment to the user agent string",
                    ArgsManager::ALLOW_ANY, OptionsCategory::DEBUG_TEST);
+    argsman.AddArg("-uaclient=<ua>", "Set user agent client name and version",
+                   ArgsManager::ALLOW_ANY, OptionsCategory::DEBUG_TEST);
 
     SetupChainParamsBaseOptions(argsman);
 
@@ -2292,8 +2294,32 @@
         }
         uacomments.push_back(cmt);
     }
+    if (args.IsArgSet("-uaclient")) {
+        const std::string ua = args.GetArg("-uaclient", "");
+        size_t colonpos = ua.find(':');
+        if (std::string::npos == colonpos) {
+            return InitError(strprintf(
+                _("-uaclient (%s) must be of form ClientName:Version."), ua));
+        }
+        const std::string name = ua.substr(0, colonpos);
+        const std::string version =
+            ua.substr(colonpos + 1, ua.size() - colonpos - 1);
+        if (name != SanitizeString(name, SAFE_CHARS_UA_COMMENT)) {
+            return InitError(strprintf(
+                _("-uaclient client name (%s) contains invalid characters."),
+                name));
+        }
+        if (version != SanitizeString(version, SAFE_CHARS_UA_COMMENT)) {
+            return InitError(strprintf(_("-uaclient client version (%s) "
+                                         "contains invalid characters."),
+                                       version));
+        }
+    }
     const std::string strSubVersion =
-        FormatSubVersion(CLIENT_NAME, CLIENT_VERSION, uacomments);
+        args.IsArgSet("-uaclient")
+            ? FormatSubVersionUserAgent(args.GetArg("-uaclient", ""),
+                                        uacomments)
+            : FormatSubVersion(CLIENT_NAME, CLIENT_VERSION, uacomments);
     if (strSubVersion.size() > MAX_SUBVERSION_LENGTH) {
         return InitError(strprintf(
             _("Total length of network version string (%i) exceeds maximum "
diff --git a/src/net.cpp b/src/net.cpp
--- a/src/net.cpp
+++ b/src/net.cpp
@@ -3155,8 +3155,9 @@
     }
 
     // Size compliance is checked at startup, it is safe to not check it again
-    std::string subversion =
-        FormatSubVersion(CLIENT_NAME, CLIENT_VERSION, uacomments);
-
-    return subversion;
+    if (gArgs.IsArgSet("-uaclient")) {
+        return FormatSubVersionUserAgent(gArgs.GetArg("-uaclient", ""),
+                                         uacomments);
+    }
+    return FormatSubVersion(CLIENT_NAME, CLIENT_VERSION, uacomments);
 }
diff --git a/test/functional/feature_uaclient.py b/test/functional/feature_uaclient.py
new file mode 100755
--- /dev/null
+++ b/test/functional/feature_uaclient.py
@@ -0,0 +1,77 @@
+#!/usr/bin/env python3
+# Copyright (c) 2021 The Bitcoin developers
+# Distributed under the MIT software license, see the accompanying
+# file COPYING or http://www.opensource.org/licenses/mit-license.php.
+"""Test the -uaclient option."""
+
+import re
+
+from test_framework.test_framework import BitcoinTestFramework
+from test_framework.test_node import ErrorMatch
+from test_framework.util import assert_equal
+
+
+class UseragentTest(BitcoinTestFramework):
+    def set_test_params(self):
+        self.num_nodes = 1
+        self.setup_clean_chain = True
+
+    def run_test(self):
+        self.log.info("test -uaclient")
+        default_useragent = self.nodes[0].getnetworkinfo()["subversion"]
+        expected = "/Bitcoin ABC:"
+        assert_equal(default_useragent[:len(expected)], expected)
+
+        self.restart_node(0, ["-uaclient=Foo Client:2000"])
+        foo_ua = self.nodes[0].getnetworkinfo()["subversion"]
+        expected = "/Foo Client:2000"
+        assert_equal(foo_ua[:len(expected)], expected)
+
+        self.log.info(
+            "non-numeric version allowed (although not recommended in BIP14)")
+        self.restart_node(0, ["-uaclient=Foo Client:Version Two"])
+        foo_ua = self.nodes[0].getnetworkinfo()["subversion"]
+        expected = "/Foo Client:Version Two"
+        assert_equal(foo_ua[:len(expected)], expected)
+
+        self.log.info("test -uaclient doesn't break -uacomment")
+        self.restart_node(0, ["-uaclient=Bar Client:3000",
+                              "-uacomment=spam bacon and eggs"])
+        bar_ua = self.nodes[0].getnetworkinfo()["subversion"]
+        expected = "/Bar Client:3000"
+        assert_equal(bar_ua[:len(expected)], expected)
+        assert "spam bacon and eggs" in bar_ua
+
+        self.log.info("test -uaclient doesn't have form Name:Version")
+        self.stop_node(0)
+        expected = r"Error: -uaclient \(spam\) must be of form ClientName:Version\."
+        self.nodes[0].assert_start_raises_init_error(
+            ["-uaclient=spam"], expected, match=ErrorMatch.FULL_REGEX)
+
+        self.log.info("test -uaclient multiple colons")
+        self.stop_node(0)
+        expected = r"Error: -uaclient client version \(2:3\) contains invalid characters\."
+        self.nodes[0].assert_start_raises_init_error(
+            ["-uaclient=spam:2:3"], expected, match=ErrorMatch.FULL_REGEX)
+
+        self.log.info("test -uaclient max length")
+        expected = r"Error: Total length of network version string \([0-9]+\) exceeds maximum length \([0-9]+\)\. Reduce the number or size of uacomments\."
+        self.nodes[0].assert_start_raises_init_error(
+            ["-uaclient=" + "a" * 256 + ":3000"], expected, match=ErrorMatch.FULL_REGEX)
+
+        self.log.info("test -uaclient invalid characters")
+        for invalid_char in ['/', '(', ')', '*', '!', '₿', '🏃']:
+            # for client name
+            expected = r"Error: -uaclient client name \(" + \
+                re.escape(invalid_char) + r"\) contains invalid characters\."
+            self.nodes[0].assert_start_raises_init_error(
+                ["-uaclient=" + invalid_char + ":Version"], expected, match=ErrorMatch.FULL_REGEX)
+            # for client version
+            expected = r"Error: -uaclient client version \(" + \
+                re.escape(invalid_char) + r"\) contains invalid characters\."
+            self.nodes[0].assert_start_raises_init_error(
+                ["-uaclient=Name:" + invalid_char], expected, match=ErrorMatch.FULL_REGEX)
+
+
+if __name__ == '__main__':
+    UseragentTest().main()