How To Write A Letter To Be A Guest Speaker . Include date for a response. Estimated time for them to deliver their speech. 8 formal Invitation Letter for Guest Speaker SampleTemplatess from www.sampletemplatess.com Whether you are organizing a special event, business conference, or graduation ceremony, the speakers and performers you invite will be among the primary attractions. Outline the subject for invitee’s speech in detail. Information about the event to which the addressee is invited: