Justin Warren Dunn (born September 22, 1995) is an American professional baseball pitcher in the Chicago White Sox organization.

Dunn was born in Freeport, New York to Ed, a grant administrator, and Donna, a health company recruiter.

As an eighth grader, he was noticed playing at a showcase with the Boys Club of New York by the baseball coach of The Gunnery, a boarding school in Washington, Connecticut.

He signed with the Mets and was assigned to the Brooklyn Cyclones, where he spent all of 2016, posting a 1–1 record with a 1.50 ERA in 11 games (eight starts).

[9] On December 3, 2018, the Mets traded Dunn, Jay Bruce, Jarred Kelenic, Anthony Swarzak, and Gerson Bautista to the Seattle Mariners for Edwin Díaz, Robinson Canó, and $20 million.

[17] On March 14, 2022, the Mariners traded Dunn, Jake Fraley, Brandon Williamson, and a player to be named later (Connor Phillips) to the Cincinnati Reds in exchange for Eugenio Suárez and Jesse Winker.

[18][19] Dunn began his Reds tenure on the 60-day injured list, with a report noting that the same shoulder strain from 2021 would keep him shelved for months.

[21] On March 4, 2023, it was announced that Dunn would be shut down for “a couple of months” so he could recover from inflammation in the right subscapularis muscle of his rotator cuff.