If you can use TextBlock
, it can be done without any converter in place with only XAML.
<TextBlock>
<TextBlock.Text>
<MultiBinding StringFormat="{}{0}, {1}">
<Binding Path="Property1"/>
<Binding Path="Property2"/>
</MultiBinding>
</TextBlock.Text>
</TextBlock>
But it won't work for Label because, it uses Content property and not Text. Hence StringFormat can't be applied.
For Label
you have to use IMultiValueConverter
. Like mentioned in comments try re-compiling your project because posted code seems fine.