At least some content in this article is derived from information featured in Fantastic Beasts: Cases from the Wizarding World. Spoilers will be present within the article.
Jeremiah Garnet was a wizard radio reporter for the Wizarding Wireless Network. He was investigating a fire at the Boathouse of Hogwarts School of Witchcraft and Wizardry and believed it to be caused by a dragon. His zealousness to develop this story led him to fake a photograph of a dragon flying over Hogwarts. This forgery was discovered by Mathilda Grimblehawk and her partner during their investigation of the fire.
Garnet managed to capture the beast responsible for the fire and sent it to Wizarding Wireless Network studios for an exclusive report, but Mathilda and her partner managed to rescue the beast and relocate it.
In addition to reporting, Garnet was also working on Hogwarts Castle: A History of Cultivated Fungus.