A narrative designer, or interactive narrative designer, is a role in contemporary video game development, the focus of which is to design the narrative elements of a game based on how players interact with its story, which differentiates it from video game writing.
In their 2018 talk at the Game Developers Conference, writer and narrative designer duo Molly Maloney and Eric Stirpe describe the difference as one where the writer focuses on the characters within the game, while the designer focuses on the player's experience of the story of the game.  Thus the role of the narrative designer in interactive storytelling is unique in that it is an active process to create story through a player's navigation of a dataspace. The confusion about the role comes from it being used interchangeably to describe roles like content designer, quest designer and game writer, due to the relative overlap in their activities. In smaller game development studios, narrative designers will often be tasked pick up these responsibilities interchangeably, as well as co-directing voice acting and sometimes even motion capture recordings.
Because of this, narrative designers need to actively collaborate with many other departments to coordinate their efforts towards a unified narrative vision. In larger game development studios this task is often also overseen by a narrative director. 
Function within game writing
Within game writing, the term narrative design has also been used to describe a planning phase that a writer goes through when they are hired in an advanced stage of a project's development. By this time, when a project has already taken shape, the writer tends to start their work by first making an inventory of all the available spaces and means through which the story can be told. Such as how many cutscenes are planned, how many lines of dialogue can be displayed in a speech bubble, how many environments and characters are expected to be in the game and so forth. This process helps a writer get a better insight into the project's available story space and thus a better understanding about how the existing gameplay experience can be enhanced through storytelling. 
Outside of game development
The idea of narrative design was perhaps first used in 1997 by Madison Smartt Bell in the context of writing books. His book, "Narrative Design: A Writer's Guide to Structure" describes a practical, structuralist approach to story creation in a manner similar to how a designer would. 
It should therefore come as no surprise that narrative design is also commonly applied within fields like industrial design, product design, architecture, marketing and experience design. Here, narrative theory is used to enhance or influence the user's experience of a product, service or messaging campaign in order to create additional value.  
However, despite how these various practices are purposefully referred to as narrative design, it is uncommon for writers or designers outside of the game development sphere to exclusively market themselves as narrative designers professionally.
- Molly Maloney and Eric Stirpe (2018). "Writing and Narrative Design: A Relationship", GDC talk, published on YouTube in 2020.
- Batchelor, James (2021). "How to get a job as a narrative director", gamesindustry.biz article.
- Suckling, Maurice (2012). Video game writing : from macro to micro. Dulles, Va.: Mercury Learning and Information. p. 85. ISBN 9781936420155.
- Bell, Madison Smartt. Narrative Design: A Writer's Guide to Structure, W.W. Norton, 1997
- Grimaldi, Silvia; Fokkinga, Steven; Ocnarescu, Ioana (2013). "Narratives in design: a study of the types, applications and functions of narratives in design practice". Proceedings of the 6th International Conference on Designing Pleasurable Products and Interfaces - DPPI '13: 201. doi:10.1145/2513506.2513528. S2CID 28074874.
- Murphy, Christopher. "Narrative Design: Principles of UX Design Pt. 3". Adobe XD Ideas. Adobe. Retrieved 9 August 2021.