<Grid Margin="20" VerticalAlignment="Top" HorizontalAlignment="Stretch">

 <Grid.RowDefinitions>

    <RowDefinition />

    <RowDefinition />

 </Grid.RowDefinitions>

 

 <Grid.ColumnDefinitions>

    <ColumnDefinition Width="*"/>

    <ColumnDefinition Width="*"/>

 </Grid.ColumnDefinitions>

 <TextBlock  Grid.Row="0" Grid.Column="0" Margin="0,0,10,0" x:Name="TxtBocCodeTiers" Text="{Binding m_strCode}" FontWeight="Bold" FontSize="22" />

 <TextBlock  Grid.Row="0" Grid.Column="1" Margin="0,0,10,0" x:Name="TxtBocNomTiers" Text="{Binding m_strNom}"   FontWeight="Bold" FontSize="22" />

 <TextBlock Grid.Row="1" Grid.Column="0" Margin="0,0,10,0" x:Name="TxtBocCPostal" TextWrapping="Wrap" Text="{Binding m_strFonction}" />

</Grid>

I know i need to use ColumnSpan but i tried and no result :(

Thank You!