The set up:

To make this work you will need to build out the following:

1. Custom field on the Campaign Members object
2. Custom field on the Campaign object
3. Workflow rule to trigger when a member is added to the campaign
4. E-mail Alert Action for the Workflow Rule
5. E-mail template to be used when the email is sent

Let’s start with the custom fields.

For this concept we are going to add a reminder date field to the Campaign object. The expectation is that this field will be populated with the date you want the reminder to go out and that this field will be populated before you add campaign members. As with most things in Salesforce you can tweak this as needed. Set up a field with the same parameters as below:

This field will need to be on the page layout and editable by users who are able to modify the campaign data.

Now on to the field on the Campaign Member object. Set up the field with the same parameters as below.

This field does not need to be visible or on a page layout. It’s just there to bring the Campaign Reminder field over to the Campaign Member object so you can use it in the Time Dependent criteria on your rule.

Now we can set up our Workflow rule. Create a new rule for the Campaign Member object with the same parameters as below.

Save the rule and then add your Time-Dependent Workflow Actions. For the purpose of this test you want your time trigger to be 0 Days After Campaign Member: Campaign Reminder. That way the rule will trigger on the date listed in the Campaign Reminder field.  If you set it up properly your time trigger section will look like this:

Now, before you go adding your action to the rule let’s do a quick test and make sure the rule is firing properly. First things first, make sure your rule is Activated! All activated now? Awesome. Next go to an existing campaign and add a date to the Campaign Reminder field. Be sure to make it a future date. Save the record and then go to Manage Members>Add Members – Search. Grab some random Contacts and add them to the Campaign. Don’t worry about what Contacts you are adding, after all you are in your sandbox or developer box, right? Once the Contacts have been added go to Setup>Monitor>Time-Based Workflow.  If you have other Time Based Workflows active in your org you may need to filter down so you only get the results for the new rule; if not, just click search.  You should now see something similar to the below screen.

In my test I added 4 Contacts and my reminder date was 3/31/2014. Based on what I am seeing there I know it worked. Awesome, right? Now we can finish the setup.

The next step is to create your email template. I am not going to get into setting up a template in this post but you can learn more if need be here.

Once the template is done navigate back to your Workflow rule and add an Action to your Time Based trigger. You will want to set up the email alert similar to the below screenshot.

Keep in mind you will need to substitute in your template in the Email Template look up. The key point here is you need to make sure you are searching on Email Field under Recipient Type and that you add the Email Field: Email to the Selected Recipients. This also means that your contacts/leads need to have a valid email for this to work. Of course your data is clean and up to date, right?

That’s it! You have now successfully set up a rule that will remind your campaign members of a pending event or whatever you want to remind them about. Keep in mind there are some limits you need to be aware of but they are mostly generous so you should be okay in most instances.