How to create/make rounded corner buttons in WPF?

I know this post is super old, but I have an answer that's surprisingly missing from the above and is also much simpler than most.

<Button>
    <Button.Resources>
        <Style TargetType="Border">
            <Setter Property="CornerRadius" Value="5"/>
        </Style>
    </Button.Resources>
</Button>

Since the default ControlTemplate for the Button control uses a Border element, adding a style for Border to the Button's resources applies that style to that Border. This lets you add rounded corners without having to make your own ControlTemplate and without any code. It also works on all varieties of Button (e.g. ToggleButton and RepeatButton).

You have to create your own ControlTemplate for the Button. just have a look at the sample

created a style called RoundCorner and inside that i changed rather created my own new Control Template with Border (CornerRadius=8) for round corner and some background and other trigger effect. If you have or know Expression Blend it can be done very easily.

<Style x:Key="RoundCorner" TargetType="{x:Type Button}">
    <Setter Property="HorizontalContentAlignment" Value="Center"/>
    <Setter Property="VerticalContentAlignment" Value="Center"/>
    <Setter Property="Padding" Value="1"/>
    <Setter Property="Template">
        <Setter.Value>
            <ControlTemplate TargetType="{x:Type Button}">
                <Grid x:Name="grid">
                    <Border x:Name="border" CornerRadius="8" BorderBrush="Black" BorderThickness="2">
                        <Border.Background>
                            <RadialGradientBrush GradientOrigin="0.496,1.052">
                                <RadialGradientBrush.RelativeTransform>
                                    <TransformGroup>
                                        <ScaleTransform CenterX="0.5" CenterY="0.5" 
                                                        ScaleX="1.5" ScaleY="1.5"/>
                                        <TranslateTransform X="0.02" Y="0.3"/>
                                    </TransformGroup>
                                </RadialGradientBrush.RelativeTransform>
                                <GradientStop Offset="1" Color="#00000000"/>
                                <GradientStop Offset="0.3" Color="#FFFFFFFF"/>
                            </RadialGradientBrush>
                        </Border.Background>
                        <ContentPresenter HorizontalAlignment="Center"
                                          VerticalAlignment="Center"
                                          TextElement.FontWeight="Bold">
                        </ContentPresenter>
                    </Border>

                </Grid>
                <ControlTemplate.Triggers>
                    <Trigger Property="IsPressed" Value="True">
                        <Setter Property="Background" TargetName="border">
                            <Setter.Value>
                                <RadialGradientBrush GradientOrigin="0.496,1.052">
                                    <RadialGradientBrush.RelativeTransform>
                                        <TransformGroup>
                                            <ScaleTransform CenterX="0.5" CenterY="0.5" ScaleX="1.5" ScaleY="1.5"/>
                                            <TranslateTransform X="0.02" Y="0.3"/>
                                        </TransformGroup>
                                    </RadialGradientBrush.RelativeTransform>
                                    <GradientStop Color="#00000000" Offset="1"/>
                                    <GradientStop Color="#FF303030" Offset="0.3"/>
                                </RadialGradientBrush>
                            </Setter.Value>
                        </Setter>
                    </Trigger>
                    <Trigger Property="IsMouseOver" Value="True">
                        <Setter Property="BorderBrush" TargetName="border" Value="#FF33962B"/>
                    </Trigger>
                    <Trigger Property="IsEnabled" Value="False">
                        <Setter Property="Opacity" TargetName="grid" Value="0.25"/>
                    </Trigger>

                </ControlTemplate.Triggers>
            </ControlTemplate>
        </Setter.Value>
    </Setter>
</Style>

Using

<Button Style="{DynamicResource RoundCorner}" 
        Height="25" 
        VerticalAlignment="Top" 
        Content="Show" 
        Width="100" 
        Margin="5" />