Is it possible to use Triggers on Grid RowDefinitions?

I think the only problem with your Xaml code is that you're overwriting the DataTrigger by setting Height explictly on the RowDefinition. Try with using a Setter instead

<RowDefinition>    <RowDefinition.Style>        <Style>            <Setter Property="RowDefinition.Height" Value="2*"/>            <Style.Triggers>                <DataTrigger Binding="{Binding Path=ShowSection}" Value="True">                    <Setter Property="RowDefinition.Height" Value="2*"/>                </DataTrigger>                <DataTrigger Binding="{Binding Path=ShowSection}" Value="False">                    <Setter Property="RowDefinition.Height" Value="0"/>                </DataTrigger>            </Style.Triggers>        </Style>    </RowDefinition.Style></RowDefinition>

I know this post is 3 years old, but still it might help someone.

<RowDefinition>    <RowDefinition.Style>        <Style TargetType="RowDefinition">            <Style.Triggers>                <DataTrigger Binding="{Binding Path=ShowSection}" Value="True">                    <Setter Property="Height" Value="2*"/>                </DataTrigger>                <DataTrigger Binding="{Binding Path=ShowSection}" Value="False">                    <Setter Property="Height" Value="0"/>                </DataTrigger>            </Style.Triggers>        </Style>    </RowDefinition.Style></RowDefinition>

I was in same situation, i managed to get it working by setting TargetType to RowDefinition.