diff --git a/src/main/java/jenkins/plugins/slack/pipeline/SlackUploadFileRunner.java b/src/main/java/jenkins/plugins/slack/pipeline/SlackUploadFileRunner.java
index 7c886f00..0c0b55bc 100644
--- a/src/main/java/jenkins/plugins/slack/pipeline/SlackUploadFileRunner.java
+++ b/src/main/java/jenkins/plugins/slack/pipeline/SlackUploadFileRunner.java
@@ -15,25 +15,29 @@
 import jenkins.plugins.slack.HttpClient;
 import jenkins.security.MasterToSlaveCallable;
 import org.apache.http.HttpEntity;
+import org.apache.http.HttpStatus;
 import org.apache.http.client.ResponseHandler;
+import org.apache.http.client.methods.CloseableHttpResponse;
 import org.apache.http.client.methods.HttpUriRequest;
 import org.apache.http.client.methods.RequestBuilder;
 import org.apache.http.entity.ContentType;
+import org.apache.http.entity.StringEntity;
 import org.apache.http.entity.mime.HttpMultipartMode;
 import org.apache.http.entity.mime.MultipartEntityBuilder;
 import org.apache.http.impl.client.CloseableHttpClient;
 import org.apache.http.util.EntityUtils;
+import org.json.JSONArray;
 import org.json.JSONObject;
 
 public class SlackUploadFileRunner extends MasterToSlaveCallable<Boolean, Throwable> implements Serializable {
 
     private static final long serialVersionUID = 1L;
-    private static final String API_URL = "https://slack.com/api/files.upload";
+    private static final String GET_UPLOAD_URL_API = "https://slack.com/api/files.getUploadURLExternal";
     private static final Logger logger = Logger.getLogger(SlackUploadFileRunner.class.getName());
     private static final String UPLOAD_FAILED_TEMPLATE = "Slack upload may have failed. Response: ";
 
     private final FilePath filePath;
-    private String fileToUploadPath;
+    private final String fileToUploadPath;
 
     private final String channels;
 
@@ -55,9 +59,9 @@ public SlackUploadFileRunner(TaskListener listener, ProxyConfiguration proxy, Sl
 
     @Override
     public Boolean call() throws Throwable {
-        logger.info(filePath + "");
-        logger.info(fileToUploadPath);
-        listener.getLogger().println(String.format("Using dirname=%s and includeMask=%s", filePath.getRemote(), fileToUploadPath));
+        logger.fine(filePath + "");
+        logger.fine(fileToUploadPath);
+        listener.getLogger().printf("Using dirname=%s and includeMask=%s%n", filePath.getRemote(), fileToUploadPath);
 
         final List<File> files = new ArrayList<>();
         new DirScanner.Glob(fileToUploadPath, null).scan(new File(filePath.getRemote()), new FileVisitor() {
@@ -79,59 +83,166 @@ public void visit(File file, String relativePath) {
     }
 
     private boolean doIt(List<File> files) {
-            CloseableHttpClient client = HttpClient.getCloseableHttpClient(proxy);
-            String threadTs = null;
-            String theChannels = channels;
-
-            //thread_ts is passed once with roomId: Ex: roomId:threadTs
-            String[] splitThread = channels.split(":", 2);
-            if (splitThread.length == 2) {
-                theChannels = splitThread[0];
-                threadTs = splitThread[1];
-            }
-            for (File file:files) {
-                 MultipartEntityBuilder multipartEntityBuilder = MultipartEntityBuilder.create()
+        String threadTs = null;
+        String theChannels = channels;
+
+        //thread_ts is passed once with roomId: Ex: roomId:threadTs
+        String[] splitThread = channels.split(":", 2);
+        if (splitThread.length == 2) {
+            theChannels = splitThread[0];
+            threadTs = splitThread[1];
+        }
+
+        List<String> fileIds = new ArrayList<>();
+        try (CloseableHttpClient client = HttpClient.getCloseableHttpClient(proxy)) {
+            for (File file : files) {
+                MultipartEntityBuilder multipartEntityBuilder = MultipartEntityBuilder.create()
                         .setMode(HttpMultipartMode.BROWSER_COMPATIBLE)
-                        .addTextBody("channels", theChannels, ContentType.DEFAULT_TEXT)
                         .addBinaryBody("file", file, ContentType.DEFAULT_BINARY, file.getName());
-
-                if (initialComment != null) {
-                   multipartEntityBuilder = multipartEntityBuilder
-                           .addTextBody("initial_comment", initialComment, ContentType.DEFAULT_TEXT);
+                JSONObject getUploadUrlResult = getUploadUrlExternal(file, client);
+                if (getUploadUrlResult == null) {
+                    return false;
                 }
 
-                if (threadTs != null) {
-                    multipartEntityBuilder = multipartEntityBuilder
-                            .addTextBody("thread_ts", threadTs, ContentType.DEFAULT_TEXT);
-                }
+                String uploadUrl = getUploadUrlResult.getString("upload_url");
 
-                HttpUriRequest request = RequestBuilder
-                        .post(API_URL)
-                        .setEntity(multipartEntityBuilder.build())
-                        .addHeader("Authorization", "Bearer " + token)
-                        .build();
-                ResponseHandler<JSONObject> responseHandler = response -> {
-                    int status = response.getStatusLine().getStatusCode();
-                    if (status >= 200 && status < 300) {
-                        HttpEntity entity = response.getEntity();
-                        return entity != null ? new org.json.JSONObject(EntityUtils.toString(entity)) : null;
-                    } else {
-                        logger.log(Level.WARNING, UPLOAD_FAILED_TEMPLATE + status);
-                        return null;
-                    }
-                };
-                try {
-                    org.json.JSONObject responseBody = client.execute(request, responseHandler);
-                    if (responseBody != null && !responseBody.getBoolean("ok")) {
-                        listener.getLogger().println(UPLOAD_FAILED_TEMPLATE + responseBody.toString());
-                        return false;
-                    }
-                } catch (IOException e) {
-                    String msg = "Exception uploading files '" + file + "' to Slack ";
-                    logger.log(Level.WARNING, msg, e);
-                    listener.getLogger().println(msg + e.getMessage());
+                if (!uploadFile(uploadUrl, multipartEntityBuilder, client)) {
+                    listener.getLogger().println("Failed to upload file to Slack");
+                    return false;
                 }
+                String fileId = getUploadUrlResult.getString("file_id");
+                fileIds.add(fileId);
+            }
+            String channelId = convertChannelNameToId(theChannels, client);
+            if (!completeUploadExternal(channelId, threadTs, fileIds, client)) {
+                listener.getLogger().println("Failed to complete uploading file to Slack");
+                return false;
             }
+
+        } catch (IOException e) {
+            String msg = "Exception uploading to Slack ";
+            logger.log(Level.WARNING, msg, e);
+            listener.getLogger().println(msg + e.getMessage());
+        }
+        return true;
+    }
+
+    private boolean completeUploadExternal(String channelId, String threadTs, List<String> fileIds, CloseableHttpClient client) throws IOException {
+        JSONObject jsonObject = new JSONObject();
+        jsonObject.put("channel_id", channelId);
+        if (initialComment != null) {
+            jsonObject.put("initial_comment", initialComment);
+        }
+        if (threadTs != null) {
+            jsonObject.put("thread_ts", threadTs);
+        }
+
+        jsonObject.put("files", convertListToJsonArray(fileIds));
+        HttpUriRequest completeRequest = RequestBuilder
+                .post("https://slack.com/api/files.completeUploadExternal")
+                .setEntity(new StringEntity(jsonObject.toString(), ContentType.APPLICATION_JSON))
+                .addHeader("Authorization", "Bearer " + token)
+                .build();
+
+        JSONObject completeRequestResponse = client.execute(completeRequest, getStandardResponseHandler());
+
+        if (completeRequestResponse != null && !completeRequestResponse.getBoolean("ok")) {
+            listener.getLogger().println(UPLOAD_FAILED_TEMPLATE + completeRequestResponse);
+            return false;
+        }
+
         return true;
     }
+
+    private static JSONArray convertListToJsonArray(List<String> fileIds) {
+        JSONArray jsonArray = new JSONArray();
+        fileIds.stream()
+                .map(fileId -> new JSONObject().put("id", fileId))
+                .forEach(jsonArray::put);
+        return jsonArray;
+    }
+
+    private static ResponseHandler<JSONObject> getStandardResponseHandler() {
+        return response -> {
+            int status = response.getStatusLine().getStatusCode();
+            if (status >= 200 && status < 300) {
+                HttpEntity entity = response.getEntity();
+                return entity != null ? new JSONObject(EntityUtils.toString(entity)) : null;
+            } else {
+                logger.log(Level.WARNING, UPLOAD_FAILED_TEMPLATE + status);
+                return null;
+            }
+        };
+    }
+
+    private String convertChannelNameToId(String channels, CloseableHttpClient client) throws IOException {
+        return convertChannelNameToId(channels, client, null);
+    }
+
+    private String convertChannelNameToId(String channelName, CloseableHttpClient client, String cursor) throws IOException {
+        RequestBuilder requestBuilder = RequestBuilder.get("https://slack.com/api/conversations.list")
+                .addHeader("Authorization", "Bearer " + token)
+                .addParameter("exclude_archived", "true")
+                .addParameter("types", "public_channel,private_channel");
+
+        if (cursor != null) {
+            requestBuilder.addParameter("cursor", cursor);
+        }
+        ResponseHandler<JSONObject> standardResponseHandler = getStandardResponseHandler();
+        JSONObject result = client.execute(requestBuilder.build(), standardResponseHandler);
+
+        if (result == null || !result.getBoolean("ok")) {
+            return null;
+        }
+
+        JSONArray channelsArray = result.getJSONArray("channels");
+        for (int i = 0; i < channelsArray.length(); i++) {
+            JSONObject channel = channelsArray.getJSONObject(i);
+            if (channel.getString("name").equals(channelName)) {
+                return channel.getString("id");
+            }
+        }
+
+        cursor = result.getJSONObject("response_metadata").getString("next_cursor");
+        if (cursor != null && !cursor.isEmpty()) {
+            return convertChannelNameToId(channelName, client, cursor);
+        }
+
+        listener.getLogger().println("Couldn't find channel id for channel name " + channelName);
+
+        return null;
+    }
+
+    private boolean uploadFile(String uploadUrl, MultipartEntityBuilder multipartEntityBuilder, CloseableHttpClient client) throws IOException {
+        HttpUriRequest request = RequestBuilder
+                .post(uploadUrl)
+                .setEntity(multipartEntityBuilder.build())
+                .addHeader("Authorization", "Bearer " + token)
+                .build();
+
+        try (CloseableHttpResponse responseBody = client.execute(request)) {
+            if (responseBody.getStatusLine().getStatusCode() != HttpStatus.SC_OK) {
+                listener.getLogger().println(UPLOAD_FAILED_TEMPLATE + EntityUtils.toString(responseBody.getEntity()));
+                return false;
+            }
+        }
+        return true;
+    }
+
+    private JSONObject getUploadUrlExternal(File file, CloseableHttpClient client) throws IOException {
+        HttpUriRequest getUploadApiRequest = RequestBuilder.get(GET_UPLOAD_URL_API)
+                .addParameter("filename", file.getName())
+                .addParameter("length", String.valueOf(file.length()))
+                .addHeader("Authorization", "Bearer " + token)
+                .build();
+        JSONObject getUploadRequestResponse = client.execute(getUploadApiRequest, getStandardResponseHandler());
+        if (getUploadRequestResponse != null && !getUploadRequestResponse.getBoolean("ok")) {
+            listener.getLogger().println(UPLOAD_FAILED_TEMPLATE + getUploadRequestResponse);
+            return null;
+        } else if (getUploadRequestResponse == null) {
+            listener.getLogger().println(UPLOAD_FAILED_TEMPLATE);
+            return null;
+        }
+        return getUploadRequestResponse;
+    }
 }
diff --git a/src/main/resources/jenkins/plugins/slack/pipeline/SlackUploadFileStep/help-channel.html b/src/main/resources/jenkins/plugins/slack/pipeline/SlackUploadFileStep/help-channel.html
index 765fc6e0..4c57d7f5 100644
--- a/src/main/resources/jenkins/plugins/slack/pipeline/SlackUploadFileStep/help-channel.html
+++ b/src/main/resources/jenkins/plugins/slack/pipeline/SlackUploadFileStep/help-channel.html
@@ -1,6 +1,5 @@
 <div>
     Allows overriding the Slack Plugin channel specified in the global configuration.
-    Multiple channels may be provided as a comma separated string.
     <br>
     <code>slackUploadFile channel: "#channel-name", filePath: "file.txt"</code>
 </div>