We'll detail everything you need to know about how to invite a guest speaker, from the earliest planning stages to drafting a formal speaker invitation letter. 1. Open the document in the editor.I am writing to ask whether you would be willing to present a talk at the conference as an invited speaker. Invited talks will be one hour long. Data Visualization: A concise summary of the event, its target audience, and expected outcomes (e.g. I am writing this letter to inform you about the upcoming__( mention the occasion or the event) It has been a while since we all have met up. Format the invitation as you would a formal business letter. Identify potential speakers and note their credentials. Check out Invitation Letters in PDF for ideas to help you out in writing your invitation letter format. Letter Of Invitation For Guest Speaker.