Marion grew up in the fabled Mississippi Delta. Her writing life began at age thirteen with a column in the town newspaper. For twenty-five years, she taught writing and literature classes at Delta State University. Her 2024 book, All the Things We Didn't Say, includes her grandmother's 1956 memoir (published for the first time), which Barnwell both reveres and laments, and which challenged her to write her own memoir. Barnwell is editor of A Place Called Mississippi: Collected Narratives, which won a Special Achievement Award from the Mississippi Institute of Arts and Letters. She is coauthor of Touring Literary Mississippi and coeditor of Fannye Cook: Mississippi's Pioneering Conservationist. All four of her books are University Press of Mississippi publications. Her play, Rats!, was performed by her Delta State colleagues for a variety of audiences. Her essays and articles have appeared in Delta magazine and Portico, among others. Her fiction has been published in such collections as What Would Elvis Think?, Fireflies in Fruit Jars, Christmas Stories from Mississippi, and Tapestry, a Delta State literary magazine which she co-founded. Barnwell has led writing workshops across a wide spectrum of ages and stages.