To highlight text in a tkinter text widget, you can use the "tag_add" method of the text widget. First, you need to create a tag with a unique name using the "tag_configure" method. Then, you can use the "tag_add" method to apply the tag to the desired text range in the text widget. This will highlight the text with the specified tag settings. You can customize the tag settings such as foreground color, background color, font style, etc.