Django admin: How to display a field that is marked as editable=False' in the model?

Your read-only fields must be in fields also:

fields = ['title', 'author', 'content', 'published_date', 'updated_date', 'created_date']
readonly_fields = ('published_date', 'updated_date', 'created_date')

You could also set the readonly fields as editable=False in the model (django doc reference for editable here). And then in the Admin overriding the get_readonly_fields method.

# models.py
class MyModel(models.Model):
  first = models.CharField(max_length=255, editable=False)

# admin.py
class MyModelAdmin(admin.ModelAdmin):
  def get_readonly_fields(self, request, obj=None):
    return [f.name for f in obj._meta.fields if not f.editable]

With the above solution I was able to display hidden fields for several objects but got an exception when trying to add a new object.

So I enhanced it like follows:

class HiddenFieldsAdmin(admin.ModelAdmin):
def get_readonly_fields(self, request, obj=None):
    try:
        return [f.name for f in obj._meta.fields if not f.editable]
    except:
        # if a new object is to be created the try clause will fail due to missing _meta.fields
        return ""

And in the corresponding admin.py file I just had to import the new class and add it whenever registering a new model class

from django.contrib import admin
from .models import Example, HiddenFieldsAdmin

admin.site.register(Example, HiddenFieldsAdmin)

Now I can use it on every class with non-editable fields and so far I saw no unwanted side effects.

You can try this

@admin.register(AgentLinks)
class AgentLinksAdmin(admin.ModelAdmin):
    readonly_fields = ('link', )