def __init__(self, *args, **kwargs): super(MessageCheckBox, self).__init__(*args, **kwargs) self._checkbox = QCheckBox() # Set layout to include checkbox size = 9 check_layout = QVBoxLayout() check_layout.addItem(QSpacerItem(size, size)) check_layout.addWidget(self._checkbox, 0, Qt.AlignRight) check_layout.addItem(QSpacerItem(size, size)) # Access the Layout of the MessageBox to add the Checkbox layout = self.layout() layout.addLayout(check_layout, 1, 1)