Draft message object collaboration in a group-based communication platform is described. A request to generate a message object can be received from a first client associated with a first entity of a group-based communication platform. A first instance of a composition user interface, configured to enable a draft of the message object to be generated, can be presented via the first client and a request to add a second entity as a collaborator can be received. A second instance of the composition user interface can be presented via a second client of the second entity. A modification to the draft of the message object can be received and, in response to receiving the modification, the message object can be updated as presented via respective instances of the composition user interface.