diff --git a/Build/MQTTnet.nuspec b/Build/MQTTnet.nuspec
index 30406c39..1ff94d37 100644
--- a/Build/MQTTnet.nuspec
+++ b/Build/MQTTnet.nuspec
@@ -19,6 +19,7 @@
 * [Client] Fixed a memory leak when web socket based connections trying to reconnect with an offline server.
 * [Client] Fixed a memory leak when TCP based connections trying to reconnect with an offline server.
 * [Client] Fixed an issue when connecting to an invalid host (format).
+* [Client] Added support for user properties in CONNECT packet.
 * [ManagedClient] Added method to trigger PING/PONG manually (connection check etc.).
 * [MQTTnet.AspNetCore] improved compatibility with AspNetCore 3.1.
 * [MQTTnet.AspNetCore] Fixed several packaging issues with the Nuget package.
diff --git a/Source/MQTTnet/Client/Options/IMqttClientOptions.cs b/Source/MQTTnet/Client/Options/IMqttClientOptions.cs
index 822603dc..ace8028b 100644
--- a/Source/MQTTnet/Client/Options/IMqttClientOptions.cs
+++ b/Source/MQTTnet/Client/Options/IMqttClientOptions.cs
@@ -1,6 +1,8 @@
-using System;
-using MQTTnet.Client.ExtendedAuthenticationExchange;
+using MQTTnet.Client.ExtendedAuthenticationExchange;
 using MQTTnet.Formatter;
+using MQTTnet.Packets;
+using System;
+using System.Collections.Generic;
 
 namespace MQTTnet.Client.Options
 {
@@ -12,11 +14,11 @@ namespace MQTTnet.Client.Options
         IMqttExtendedAuthenticationExchangeHandler ExtendedAuthenticationExchangeHandler { get; }
         MqttProtocolVersion ProtocolVersion { get; }
         IMqttClientChannelOptions ChannelOptions { get; }
-        
+
         TimeSpan CommunicationTimeout { get; }
         TimeSpan KeepAlivePeriod { get; }
         TimeSpan? KeepAliveSendInterval { get; }
-        
+
         MqttApplicationMessage WillMessage { get; }
         uint? WillDelayInterval { get; }
 
@@ -28,5 +30,6 @@ namespace MQTTnet.Client.Options
         bool? RequestResponseInformation { get; }
         uint? SessionExpiryInterval { get; }
         ushort? TopicAliasMaximum { get; }
+        List<MqttUserProperty> UserProperties { get; set; }
     }
 }
\ No newline at end of file
diff --git a/Source/MQTTnet/Client/Options/MqttClientOptions.cs b/Source/MQTTnet/Client/Options/MqttClientOptions.cs
index c47f5c6a..a28cbfd7 100644
--- a/Source/MQTTnet/Client/Options/MqttClientOptions.cs
+++ b/Source/MQTTnet/Client/Options/MqttClientOptions.cs
@@ -1,6 +1,8 @@
-using System;
-using MQTTnet.Client.ExtendedAuthenticationExchange;
+using MQTTnet.Client.ExtendedAuthenticationExchange;
 using MQTTnet.Formatter;
+using MQTTnet.Packets;
+using System;
+using System.Collections.Generic;
 
 namespace MQTTnet.Client.Options
 {
@@ -16,7 +18,7 @@ namespace MQTTnet.Client.Options
         public TimeSpan CommunicationTimeout { get; set; } = TimeSpan.FromSeconds(10);
         public TimeSpan KeepAlivePeriod { get; set; } = TimeSpan.FromSeconds(15);
         public TimeSpan? KeepAliveSendInterval { get; set; }
-        
+
         public MqttApplicationMessage WillMessage { get; set; }
         public uint? WillDelayInterval { get; set; }
 
@@ -29,5 +31,6 @@ namespace MQTTnet.Client.Options
         public bool? RequestResponseInformation { get; set; }
         public uint? SessionExpiryInterval { get; set; }
         public ushort? TopicAliasMaximum { get; set; }
+        public List<MqttUserProperty> UserProperties { get; set; }
     }
 }
diff --git a/Source/MQTTnet/Client/Options/MqttClientOptionsBuilder.cs b/Source/MQTTnet/Client/Options/MqttClientOptionsBuilder.cs
index 316e5b57..383dbc96 100644
--- a/Source/MQTTnet/Client/Options/MqttClientOptionsBuilder.cs
+++ b/Source/MQTTnet/Client/Options/MqttClientOptionsBuilder.cs
@@ -1,6 +1,8 @@
 using MQTTnet.Client.ExtendedAuthenticationExchange;
 using MQTTnet.Formatter;
+using MQTTnet.Packets;
 using System;
+using System.Collections.Generic;
 using System.Linq;
 using System.Text;
 
@@ -116,6 +118,20 @@ namespace MQTTnet.Client.Options
             return this;
         }
 
+        public MqttClientOptionsBuilder WithUserProperty(string name, string value)
+        {
+            if (name is null) throw new ArgumentNullException(nameof(name));
+            if (value is null) throw new ArgumentNullException(nameof(value));
+
+            if (_options.UserProperties == null)
+            {
+                _options.UserProperties = new List<MqttUserProperty>();
+            }
+
+            _options.UserProperties.Add(new MqttUserProperty(name, value));
+            return this;
+        }
+
         public MqttClientOptionsBuilder WithCredentials(string username, string password = null)
         {
             byte[] passwordBuffer = null;
diff --git a/Source/MQTTnet/Formatter/V5/MqttV500DataConverter.cs b/Source/MQTTnet/Formatter/V5/MqttV500DataConverter.cs
index 886b937b..f55c3476 100644
--- a/Source/MQTTnet/Formatter/V5/MqttV500DataConverter.cs
+++ b/Source/MQTTnet/Formatter/V5/MqttV500DataConverter.cs
@@ -1,7 +1,4 @@
-using System;
-using System.Collections.Generic;
-using System.Linq;
-using MQTTnet.Client.Connecting;
+using MQTTnet.Client.Connecting;
 using MQTTnet.Client.Disconnecting;
 using MQTTnet.Client.Options;
 using MQTTnet.Client.Publishing;
@@ -11,7 +8,9 @@ using MQTTnet.Exceptions;
 using MQTTnet.Packets;
 using MQTTnet.Protocol;
 using MQTTnet.Server;
-
+using System;
+using System.Collections.Generic;
+using System.Linq;
 using MqttClientSubscribeResult = MQTTnet.Client.Subscribing.MqttClientSubscribeResult;
 
 namespace MQTTnet.Formatter.V5
@@ -127,7 +126,8 @@ namespace MQTTnet.Formatter.V5
                     RequestProblemInformation = options.RequestProblemInformation,
                     RequestResponseInformation = options.RequestResponseInformation,
                     SessionExpiryInterval = options.SessionExpiryInterval,
-                    TopicAliasMaximum = options.TopicAliasMaximum
+                    TopicAliasMaximum = options.TopicAliasMaximum,
+                    UserProperties = options.UserProperties
                 }
             };
         }
@@ -244,11 +244,11 @@ namespace MQTTnet.Formatter.V5
             {
                 // QoS 0 has no response. So we treat it as a success always.
                 // Both enums have the same values. So it can be easily converted.
-                 result.ReasonCode = (MqttClientPublishReasonCode)pubAckPacket.ReasonCode;
+                result.ReasonCode = (MqttClientPublishReasonCode)pubAckPacket.ReasonCode;
 
-                 result.PacketIdentifier = pubAckPacket.PacketIdentifier;
+                result.PacketIdentifier = pubAckPacket.PacketIdentifier;
             }
-            
+
             return result;
         }