Notable aspects of his writing style include a number of trademark affections and concepts, including:
- Unusual tonal tags, structured in a general manner like the following: he said "something something something." Emotional tone: "Something."
- Certain turns of phrase tend to show up across all of his work quite often, some particularly common ones being "butter wouldn't melt in his/her mouth" and "[insert adjective here] as you please."
- A tendency to have fun with characters' emotional and physical relationships that's somewhat unusual for most science fiction authors.
- At least one romance per book. Some of his co-writers have mentioned Flint shipping the characters the co-writer developed. He has even unabashedly shipped Historical Domain Characters that he thinks should have gotten together.
- Heavy usage of Arc Words, often in the form of a Badass Boast, or an epiphet, such as "Deadly with a blade is Belisarius"., or "Hidalgo true and pure".
- A notable bantering style of dialogue between most of the major cast, especially in a "cheerfully grim" attitude towards fighting in wars.
- A distinct tendency towards being able to make workable, interesting and entertaining omni-competent and plot-bending characters (examples: see Flavius Belisarius, Michael Stearns and Victor Cachat).
- Where the setting allows, Scots-Irish or West Virginia based characters portrayed favorably
If not the creator of the Assiti Shards time travel idea (also known as ISOT events, after the Island in the Sea of Time), then the writer of the best example. Assiti being an anagram of As It Is, and the idea is simple: a location is picked up whole and dropped in another time, with only the resources they would have on hand—As It Is—to survive.
Prior to becoming an author, Flint worked as a labor organizer and political activist, earning something of a reputation as a leftist radical. Up to the day he died he was a member of the Socialist Workers Party, one of the largest far-left parties in the United States (relatively speaking). To a casual reader this is generally not apparent—most notable is that his books generally have heroes with strong blue-collar values—but a reader schooled in Marxist theory or socialist history can pick up plenty of references. This usually confused people who considered Baen, where he held several important editorial positions, to be a conservative publishing house.note
Notable works include:
- Mother of Demons, his first published novel. Human ship crash lands on an alien world and we get to see how the two societies interact.
- 1632, the most successful and well known of the Assiti Shards concept; in 2000 AD, a West Virginia coal mining town is dropped into Germany, in the year 1632. In the middle of one of the worst wars of the past millennium. Some hilarity ensues, along with a whacking great dose of character development for pretty much everyone, romance, heroics, and death. Oh, and the American Revolution — a century or so ahead of schedule.
- Wages of Sin subseries in the larger David Weber's Honor Harrington, where one of his favorite characters, superspy Victor Cachat, comes into play.
- Trail of Glory, an Alternate History in which after the War of 1812 the Cherokee, in collaboration with freed blacks and other Native American tribes, head west decades early and found a small nation in Arkansas.
- Joe's World written with Richard Roach, a class-warfare satirical fantasy series; this is one where his aforementioned political views really come to the fore.
- The Belisarius Series, written by Flint from an outline by David Drake, in which two rival intelligences from the unimaginably distant future attempt to influence human history in sixth-century Rome and India.
- Rats, Bats and Vats series, written with Dave Freer.
- The Krim Pyramid series, also with Dave Freer.
- The Boundary series, written with Ryk E. Spoor.
- The Jao Empire series, written with K. D. Wentworth.
- The Heirs of Alexandria series, written with Dave Freer and Mercedes Lackey.
- The Karres series, sequels to The Witches of Karres by James H. Schmitz.