<Grid x:Name="LayoutRoot">
    <Canvas x:Name="canvas" Background="Transparent" Width="{Binding Width}" Height="{Binding Height}">
        <Canvas.Clip>
            <RectangleGeometry RadiusX="0" RadiusY="0" />
        </Canvas.Clip>


        <TextBlock x:Name="textBlock1"
                   Height="{Binding Height}"
                   Width="{Binding MWidth}"
                   TextWrapping="{Binding MTextWrap}"
                   Foreground="{Binding Foreground}"
                   Text="{Binding Text}"
                   TextTrimming="None"
                   FontSize="{Binding MFontSize}"/>
    </Canvas>
</Grid>

public partial class MarqueeTextBlock : UserControl
{
    // storyboard
    Storyboard storyboard;

    // offset when textBlock1 is long, because user want to see smooth scrolling
    private double offset =0;

    // default offset
    private double defaultOffset =100;

    // default velocity
    int velocity = 0;

    // whether control has beed loaded
    // because it's when control is loaded do we start marquee
    bool isLoaded = false;

    public MarqueeTextBlock()
    {
        InitializeComponent();

        Loaded += MarqueeTextBlock_Loaded;
        Unloaded += MarqueeTextBlock_Unloaded;
    }

    // unload event
    void MarqueeTextBlock_Unloaded(object sender, RoutedEventArgs e)
    {
        // stop marquee when control is unloaded
        StopMarquee();
    }

    // set data context in Loaded
    void MarqueeTextBlock_Loaded(object sender, RoutedEventArgs e)
    {
        if (!isLoaded)
        {
            // control is loaded
            isLoaded = true;

            LayoutRoot.DataContext = this;

            // resize the clipping

            Rect rect = new Rect(0, 0, 10000, canvas.ActualHeight);

            RectangleGeometry reo = new RectangleGeometry();
            reo.Rect = rect;
            this.canvas.Clip = reo;

            // always vertical alignment
            ChangeOffsetTop();

            // this is OK for marquee to start
            StartMarquee();
        }
        else
        {
            // just run it, after user come to this page again
            StartMarquee();
        }
    }


    public void StartMarquee()
    {
        // first stop all marquee
        StopMarquee();

        if (ShouldStartMarquee())
        {
            // change offset
            ChangeOffsetLeft(true);

            DoAnimationFirst();
        }
        else
        {
            // change offset
            ChangeOffsetLeft(false);
        }
    }

    public void StopMarquee()
    {
        if (storyboard != null)
        {
            storyboard.Stop();
        }
    }

    bool ShouldStartMarquee()
    {
        return textBlock1.ActualWidth > LayoutRoot.ActualWidth;
    }


    // after
    void storyboard_Completed(object sender, EventArgs e)
    {
        DoAnimationAfter();

        // remeber to unsubscribe
        storyboard.Completed += storyboard_Completed;
    }


    ////////////////////////////////////////////////////////////////////////////
    // calculate offset
    void ChangeOffsetLeft(bool isLong)
    {
        if (isLong)
        {
            offset = defaultOffset;
            Canvas.SetLeft(textBlock1, offset);
        }
        else
        {
            offset = (canvas.ActualWidth - textBlock1.ActualWidth)/2;
            Canvas.SetLeft(textBlock1, offset);
        }
    }

    // center vertical
    void ChangeOffsetTop()
    {
        double topOffset = (canvas.ActualHeight - textBlock1.ActualHeight) / 2;
        Canvas.SetTop(textBlock1, topOffset);

    }

    int CalculateDurationFirst()
    {
        int duration = 50000;



        return duration;
    }

    int CalculateDurationAfter()
    {
        int duration = 50000;



        return duration;
    }


    void DoAnimationFirst()
    {
        storyboard = new Storyboard();
        TranslateTransform trans = new TranslateTransform() { X = 5.0, Y = 1.0 };
        textBlock1.RenderTransformOrigin = new Point(0.5,0.5);
        textBlock1.RenderTransform = trans;

        // we must calculate the Duration
        DoubleAnimation moveAnim = new DoubleAnimation();
        int durationFirst = CalculateDurationFirst();
        moveAnim.Duration = TimeSpan.FromMilliseconds(durationFirst);

        moveAnim.From = 0;

        moveAnim.To = -textBlock1.ActualWidth - offset;
    //    MessageBox.Show((-textBlock1.ActualWidth-offset).ToString());

        Storyboard.SetTarget(moveAnim, textBlock1);
        Storyboard.SetTargetProperty(moveAnim, new PropertyPath("(UIElement.RenderTransform).(TranslateTransform.X)"));

        // subscribe to Completed event
        storyboard.Completed += new EventHandler(storyboard_Completed);

        storyboard.Children.Add(moveAnim);

        storyboard.FillBehavior = FillBehavior.HoldEnd;

        storyboard.Begin();
    }



    void DoAnimationAfter()
    {
        storyboard = new Storyboard();
        TranslateTransform trans = new TranslateTransform() { X = 5.0, Y = 1.0 };
        textBlock1.RenderTransformOrigin = new Point(0.5, 0.5);
        textBlock1.RenderTransform = trans;

        // we must calculate the Duration
        DoubleAnimation moveAnim = new DoubleAnimation();
        int durationAfter = CalculateDurationAfter();
        moveAnim.Duration = TimeSpan.FromMilliseconds(durationAfter);

        moveAnim.From = canvas.ActualWidth;
        moveAnim.To = (-textBlock1.ActualWidth - offset);

        Storyboard.SetTarget(moveAnim, textBlock1);
        Storyboard.SetTargetProperty(moveAnim, new PropertyPath("(UIElement.RenderTransform).(TranslateTransform.X)"));

        storyboard.Children.Add(moveAnim);
        storyboard.RepeatBehavior = RepeatBehavior.Forever;
        storyboard.FillBehavior = FillBehavior.HoldEnd;

        storyboard.Begin();
    }


    /////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////
    // dependency property
    public static readonly DependencyProperty TextProperty =
    DependencyProperty.Register("Text", typeof(string), typeof(MarqueeTextBlock), null);

    public string Text
    {
        get { return (string)this.GetValue(TextProperty); }
        set
        {
            this.SetValue(TextProperty, value);

            // this doesnot marquee for the first time
            // because textBlock1.ActualWidth is 0 !!
            if (isLoaded)
            {
                StartMarquee();
            }

        }
    }

    public static readonly DependencyProperty MFontSizeProperty = DependencyProperty.Register("MFontSize",
    typeof(int), typeof(MarqueeTextBlock), null);

    public int MFontSize
    {
        get { return (int)this.GetValue(MFontSizeProperty); }
        set
        {
            this.SetValue(MFontSizeProperty, value);
        }
    }

    public static readonly DependencyProperty MTextWrapProperty = DependencyProperty.Register("MTextWrap",
  typeof(TextWrapping), typeof(MarqueeTextBlock), null);

    public TextWrapping MTextWrap
    {
        get { return (TextWrapping)this.GetValue(MTextWrapProperty); }
        set
        {
            this.SetValue(MTextWrapProperty, value);
        }
    }

    public static readonly DependencyProperty MWidthProperty = DependencyProperty.Register("MWidth",
typeof(int), typeof(MarqueeTextBlock), null);

    public int MWidth
    {
        get { return (int)this.GetValue(MWidthProperty); }
        set
        {
            this.SetValue(MWidthProperty, value);
        }
    }
}

<controls2:MarqueeTextBlock x:Name="txtT"
                                      MFontSize="15"

                                      Height="80" Margin="0,-15,0,0" FontSize="1"
                                               />