SharePoint 2013 workflows do not have a default action to start another 2013 workflow. There is an action to start 2010 workflows, but for my solution I required the more advanced actions only available with SharePoint 2013  workflows. With the help of the call http web service action I was able to create a REST call that started the workflow. The solution was build on SharePoint Online (Office 365) using a SharePoint 2013 workflow.

The REST call workflow consist of three major parts;

1. The HTTP web service URL
2. The SubscriptionID of the workflow that needs to be started
3. The itemID of the item on which the workflows needs to be started.

A side note: The workflow that is being started needs to be configured to start manually. I could not find any reference on MSDN about this, but without this option I would get an error message.

Solution

1. Create a SharePoint 2013 workflow
2. Create a string variable called CurrentItemID
3. Create a string variable called WorkflowGUID
4. Create a string variable called regURL
   
5. Now we need to find the SubscriptionID of the workflow we want to start. It is possible to use another REST call to find the SubscriptionID. But I prefer the following method.
6. Navigate to the workflow settings of the list where the workflow is located
7. Right-click on the workflow and open the properties
8. Copy the URL and find the SubscriptionID within the URL
   
9. Set the variable WorkflowGUID with the found SubscriptionID
10. Set the variable CurrentID with the ItemID of the current item or item on which the workflow needs to start.
    
11. Then store the following URL to the variable regURL

    [%workflow Context: Current Site URL%]_api/SP.WorkflowServices.WorkflowInstanceService.Current/StartWorkflowOnListItemBySubscriptionId(subscriptionId='[%Variable: WorkflowGUID%]',itemID='[%Variable: CurrentItemID%]')
    

12. Add the Call HTTP web service to the workflow and set the “this” to the regURL
13. Set the HTTP Method to HTTP POST
    
14. The workflow will now look like this
    
15. The app step is used to make sure the workflow has the required permissions. More details about the App Stepp will be explained in another blog post.