Short Answer

Yes it's possible with WSGIMiddleware.

For example, you can use all Django features (yes admin too) with mounting, with this example code.

import os
from importlib.util import find_spec

from configurations.wsgi import get_wsgi_application
from fastapi import FastAPI
from fastapi.middleware.wsgi import WSGIMiddleware
from fastapi.staticfiles import StaticFiles

from api import router

os.environ.setdefault("DJANGO_SETTINGS_MODULE", "myapp.settings")
os.environ.setdefault("DJANGO_CONFIGURATIN", "Localdev")

application = get_wsgi_application()

app = FastAPI()
app.mount("/admin", WSGIMiddleware(application))
app.mount("/static"
    StaticFiles(
         directory=os.path.normpath(
              os.path.join(find_spec("django.contrib.admin").origin, "..", "static")
         )
   ),
   name="static",
)

Also this one is from WSGIMiddleware documentation, it's a more straight-forward example (This one is for Flask but it demonstrates the same idea.).

from fastapi import FastAPI
from fastapi.middleware.wsgi import WSGIMiddleware
from flask import Flask, escape, request

flask_app = Flask(__name__)


@flask_app.route("/")
def flask_main():
    name = request.args.get("name", "World")
    return f"Hello, {escape(name)} from Flask!"


app = FastAPI()


@app.get("/v2")
def read_main():
    return {"message": "Hello World"}


app.mount("/v1", WSGIMiddleware(flask_app))

Thank you for the awesome answers. Here is a little tweaked answer where I have fixed some imports as well as I have used a model from a Django app.

from fastapi import FastAPI
from fastapi.middleware.wsgi import WSGIMiddleware
from django.core.wsgi import get_wsgi_application
import os
from importlib.util import find_spec
from fastapi.staticfiles import StaticFiles
from django.conf import settings


# Export Django settings env variable
os.environ.setdefault('DJANGO_SETTINGS_MODULE', 'project.settings')

# Get Django WSGI app
django_app = get_wsgi_application()

# Import a model
# And always import your models after you export settings
# and you get Django WSGI app
from accounts.models import Account

# Create FasatAPI instance
app = FastAPI()

# Serve Django static files
app.mount('/static',
    StaticFiles(
         directory=os.path.normpath(
              os.path.join(find_spec('django.contrib.admin').origin, '..', 'static')
         )
   ),
   name='static',
)

# Define a FastAPI route
@app.get('/fastapi-test')
def read_main():
    return {
        'total_accounts': Account.objects.count(),
        'is_debug': settings.DEBUG 
    }

# Mount Django app
app.mount('/django-test', WSGIMiddleware(django_app))

Hint: I created a file named app.py in my Django project's root directory and it worked. Here is my directory structure:

.
├── accounts
│   ├── __init__.py
│   ├── admin.py
│   ├── apps.py
│   ├── migrations
│   │   ├── 0001_initial.py
│   │   ├── __init__.py
│   ├── models.py
│   ├── tests.py
│   └── views.py
├── app.py
├── db.sqlite3
├── project
│   ├── __init__.py
│   ├── asgi.py
│   ├── settings.py
│   ├── urls.py
│   └── wsgi.py
└── manage.py

And run your FastAPI app:

(myvenv) ➜  project uvicorn --host 0.0.0.0 --port 8000 app:app --reload
INFO:     Uvicorn running on http://0.0.0.0:8000 (Press CTRL+C to quit)
INFO:     Started reloader process [48366] using statreload
INFO:     Started server process [48368]
INFO:     Waiting for application startup.
INFO:     Application startup complete.

Hopefully, this will work for you. Now accessing /django-test will serve your Django project and /fastapi-test will serve the FastAPI part.

This configuration serves Django static files too and we can use our Django models in our FastAPI code as well. I'll test it further and I'll update this answer if I find any possibilities for improvement.

there is good resource as follows:

Combine the power of FastAPI and Django