Right click to select row in dataGridView

Try setting the current cell like this (this will set the CurrentRow property of the DataGridView before the context menu item is selected):

    private void dataGridView1_CellMouseDown(object sender, DataGridViewCellMouseEventArgs e)
    {
        var dataGrid = (DataGridView) sender;
        if (e.Button == MouseButtons.Right && e.RowIndex != -1)
        {
            var row = dataGrid.Rows[e.RowIndex];
            dataGrid.CurrentCell = row.Cells[e.ColumnIndex == -1 ? 1 : e.ColumnIndex];
            row.Selected = true;
            dataGrid.Focus();
        }
    }

I realize this thread is old, I just wanted to add one thing: If you want to be able to select, and perform the action, on multiple rows: you can check to see if the row you are right-clicking is already selected. This way the DataGridview behaves likes a ListView in this regard. So right clicking on a row not already selected: selects this row and open the context menu. Right clicking on a row already selected just gives you the context menu and keep the selected rows as expected.

 private void dataGridView1_CellMouseDown(object sender, DataGridViewCellMouseEventArgs e)
    {
        if (e.RowIndex != -1 && e.ColumnIndex != -1)
        {
            if (e.Button == MouseButtons.Right)
            {
                DataGridViewRow clickedRow = (sender as DataGridView).Rows[e.RowIndex]; 
                if (!clickedRow.Selected)
                    dataGridView1.CurrentCell = clickedRow.Cells[e.ColumnIndex];

                var mousePosition = dataGridView1.PointToClient(Cursor.Position);

                ContextMenu1.Show(dataGridView1, mousePosition);
            }
        }
    }