Step 1: Make sure your Skype client is up-to-date by going to Help > Check for updates. Once finished, completely exit Skype.
Step 2: Head to C:\users\[your user name]\App Data\Roaming\Skype\[your Skype username]. You should see a config.xml file in this directory. Right-click it and choose Edit, then find the line that says <AdvertPlaceholder> and delete the entire line. Make sure to save your changes to the file before exiting. You can use Ctrl+F to find the line quickly.

Note: If you do not see the App Data folder, it's probably because you don't have Show hidden files enabled. Click the Organize button > Folder and search options > View tab > mark the radio button next to Show hidden files, folders, or drives
Step 3: Mark the config.xml file as read-only by right-clicking the file and choosing Properties. Check the box next to Read-only and click OK.

Now your chat window and video conferences will be free of advertisements.

What do you think of the advertisement placement in chat? Share your thoughts in the comments.