You can setup Pipenv to use Conda’s Python executable and site packages directory (ref).
pipenv --python=$(conda run which python) --site-packages
You can check if you are indeed using your Conda environment in Pipenv:
pipenv run python
>>> import sys
>>> sys.executable, sys.path
# <directories under your Conda environment>
With NumPy installed through Conda, but not Pipenv, you can see that Pipenv will still find NumPy.
conda install numpy
pipenv run python
>>> import numpy as np
>>> np.__file__
# <path under your Conda environment>
When you install NumPy through Pipenv, it will shadow Conda’s installation of the the package.
pipenv install numpy
pipenv run python
>>> import numpy as np
>>> np.__file__
# <path under your Pipenv environment>