Implementations set forth herein relate to an automated assistant that facilitates the creation of complex messages from user input(s) to the automated assistant. Each message can be created according to a respective template that is selected based on user input that directs the automated assistant to communicate a message to a recipient. Furthermore, sections of a template can be designated for certain content based on prior messages communicated by one or more users to one or more recipients. In this way, in response to a user requesting that the automated assistant send a message, the automated assistant can select a related template and fill out the template accordingly. In some instances, content that is assigned to certain sections of the selected template can come from a variety of different sources and/or may not be explicitly specified in the request from the user to the automated assistant.