I'm calling Powershell like so:

C:\Windows\System32\WindowsPowerShell\v1.0\powershell.exe -noprofile -noninteractive -nologo -file "C:\Users\dummy\Documents\dev\powershell\samples\test.ps1"

I'm calling it from a python script, but the same problem can be observed if called via a shortcut. I thought the -NonInteractive flag would cause Poweshell to execute in a hidden window, but it doesn't. Is there a way of supressing the console window when calling Powershell from an external application?

Solution based on Johannes Rössel suggestion

st_inf = subprocess.STARTUPINFO()
st_inf.dwFlags = st.inf.dwFlags | subprocess.STARTF_USESHOWWINDOW
Popen(["notepad"], startupinfo=st_inf)