Start local system process with hide the window.

ProcessStart.cs

private void button1_Click(object sender, EventArgs e)
{
    // Create instance of System.Diagnostics.Process
    var proc = new System.Diagnostics.Process();

    // Set path to exe file.
    proc.StartInfo.FileName = @"[path to exe]";

    // Set argument of exe
    proc.StartInfo.Arguments = arg;

    // Hide window of command prompt
    proc.StartInfo.CreateNoWindow = true;
    proc.StartInfo.UseShellExecute = false;

    // Set to be exited event when the process terminates.
    proc.EnableRaisingEvents = true;
    proc.Exited += Proc_Exited;
    proc.Start();
}

private void Proc_Exited(object sender, EventArgs e)
{
    MessageBox.Show("Process terminated.");
}