I'm using a QTableView within a QWidget window.
Have you put this table view inside of a layout on your widget? If you have simply placed it on the widget without the layout, then there is nothing to manage its size and it won't get the information needed to automatically display the scroll bars when it is sized to be smaller than its contents.

The "solution" suggested by Gokulnathvc won't actually work if the table view is not in a layout. Yes, the scrollbar will always be visible, but the bottom of the table will still be cut off.