How to set DataGridView textbox column to multi-line?

Apart from setting WrapMode of the DefaultCellStyle, you can do the following:

1. You need to catch GridView's EditingControlShowing Event
2. Cast Control property on the EventArgs to the type you want (i.e. textbox, checkbox, or button)
3. Using that casted type, change the Multiline property like below:

private void MyGridView_EditingControlShowing(object sender, DataGridViewEditingControlShowingEventArgs e)
{
    TextBox TB = (TextBox)e.Control;
    TB.Multiline = true;            
}

    int multilineht = 0;
    private void CustGridView_EditingControlShowing(object sender, DataGridViewEditingControlShowingEventArgs e)
    {
        multilineht = CustGridView.Rows[CustGridView.CurrentCell.RowIndex].Height;
        CustGridView.AutoResizeRow(CustGridView.CurrentCell.RowIndex, DataGridViewAutoSizeRowMode.AllCells);
    }

    private void CustGridView_CellEndEdit(object sender, DataGridViewCellEventArgs e)
    {
        CustGridView.Rows[CustGridView.CurrentCell.RowIndex].Height = multilineht;
    }

If you would like to set Multiline property just for one column of your DataGridView you can do

dataGridView.Columns[0].DefaultCellStyle.WrapMode = DataGridViewTriState.True;