Second try. Didn t manage to get the previous solution attempt to behave correctly. Found an alternate way by rendering the tooltip using a custom draw method.

Setup the controls:

string tip = "aaaaaa" + Environment.NewLine + "bbb";           
toolTip1.OwnerDraw = true;
toolTip1.Draw += toolTip1_Draw;
toolTip1.SetToolTip(textBox1, tip);

Handle the draw event:

private void toolTip1_Draw(object sender, DrawToolTipEventArgs e)
{
    e.Graphics.FillRectangle(SystemBrushes.Info, e.Bounds);
    e.DrawBorder();           
    e.DrawText(TextFormatFlags.RightToLeft | TextFormatFlags.Right);
}

If it s windows forms I guess you have to rely on the unicode control characters to mark the tooltip text as RTL.

string myToolTipText = "aaaaaa"+Environment.newLine+"bbb";
char rle_char = (char)0x202B;// RLE embedding 
control.RightToLeft = RightToLeft.Yes;
control.ToolTipText = rle_char + myToolTipText;

Check this blog for more information on authoring RTL applications.

If it s a web application you can check the w3c authoring RTL applications guidelines. Basically it comes down to the same solution as for windows forms, adding RLE chars.

The ToolTip control already supports this. The key is that the control for which you display the tip has a right-to-left layout. This example form demonstrates this:

using System;
using System.Windows.Forms;

namespace WindowsFormsApplication1 {
    public partial class Form1 : Form {
        ToolTip mTip = new ToolTip();
        public Form1() {
            InitializeComponent();
            this.RightToLeft = RightToLeft.Yes;
            this.RightToLeftLayout = true;
        }
        protected override void OnMouseDown(MouseEventArgs e) {
            mTip.Show("Hi
there", this);
        }
    }
}

Just some general thoughts to give an idea about what s going on: the tooltip class does not draw text like a multiline textbox. The whole tool-tip is considered one line without a binding rectangle, hence RTL vs LTR have no meaning (other then the order of characters within the text).

Result: using normal right-to-left or left-to-right switches either with Unicode RTL codepoints or otherwise, won t help when it comes to aligning: none is applied.

One way out is (ab)using a TextBox and place it nicely over the place of the tooltip. But others have shown prettier ways with owner-drawn tooltips, which is definitely the way to go.