Man, this question takes me back to all those heated debates in online forums! The short answer is no—Harry never leaves Gryffindor for Slytherin in the official 'Harry Potter' series. But let’s dig deeper because the idea itself is fascinating. The Sorting Hat almost put him in Slytherin during his first year, which sparked endless fan theories and alternate universe stories. Some fanfics explore what might’ve happened if Harry had embraced that path, like 'Prince of Slytherin' or 'Harry Potter and the Boy Who Lived.' Those stories are wild, with darker character arcs and political maneuvering.
Still, canon Harry’s loyalty to Gryffindor never wavers. His choices define him more than the Hat’s initial suggestion, which is a recurring theme in the books. The closest we get to a 'switch' is Draco’s redemption arc in 'Cursed Child,' but even that’s controversial among fans. If you’re craving a Slytherin Harry, though, the fanfiction community has you covered—just don’t expect it from J.K. Rowling’s original work.