I'm using git-bash.exe. After installing from pypi, ran the following command on my Windows machine:

commit-message-validator install

It creates a post-commit file under the .git/hooks directory with the following content:

c:\users\a\appdata\local\programs\python\python36\python.exe c:\users\a\appdata\local\programs\python\python36\lib\site-packages\commit_message_validator\__init__.py

But in git-bash, \ is treated as escape sequence, therefore the following message is shown upon new commits:

bash: c:usersaappdatalocalprogramspythonpython36python.exe: command not found

Windows also accepts / as the path separator. I'd suggest using forward slash to make the hook compatible with git-bash.