The Bishop: Hufflepuff. The Bishop symbolizes mercy and compassion, first offering Valjean shelter for the night and then offering forgiveness after the newly-released convict attempted to rob him. He plays a small but important role, and from what we see of him (which in the novel is quite a lot, about 60 pages before Valjean shows up), I think Hufflepuff is a safe bet. Hufflepuffs are described as patient, fair, and hard-working. The Bishop is also very wise, but I don’t think Ravenclaw would be a good fit. His wisdom comes in second to his concern for his fellow man.
Jean Valjean: Gryffindor/Hufflepuff. Valjean is difficult. I can’t see him as a Ravenclaw or a Slytherin, but he has strong qualities of both remaining houses, as well as traits that seem like they should disqualify him. He has the humble benevolence of a Hufflepuff. Everything he does is to help other people, whether his sister’s children, his adopted daughter, random people he meets, or even his enemy. He’s generous, selfless, and the epitome of true fairness and mercy (whereas Javert represents rigid justice). However, he operates alone and does not allow other people to get close to him. Even Cosette: he loves her with all his heart and is always there for her to the extent of overprotectiveness, but he keeps his own past a secret even from her. It’s hard to imagine a Hufflepuff isolating themselves emotionally the way he does. For a Gryffindor, on the other hand, it wouldn’t be surprising. Harry himself shows the tendency to cut himself off from others rather than risk putting them in danger; this can be seen in his break-up with Ginny, as well as the early chapters of Deathly Hallows, when he contemplates leaving Ron and Hermione behind to protect them from Voldemort. There’s certainly a courageous element to Valjean’s selflessness. He’s more than willing to put himself in danger for the sake of others. As a prisoner, he once risked his life to rescue a fellow convict who the guards were prepared to let die. As Mayor, he was willing to give up his freedom and comfortable life to save an innocent man from being convicted in his place. Near the end of the novel, he even sneaks into the battle at the barricade to save the life of his daughter’s beloved, knowing such a move could easily get him killed. And yet, he does this because he feels such a strong loyalty to humanity as a whole, not because he’s trying to play the hero. Here’s where I keep going in circles: these actions could be Gryffindor, but his reasons seem more Hufflepuff, and he fits pretty well into Hufflepuff, except where he seems more Gryffindor.
Javert: Hufflepuff. I’ve already written about this here, but Javert cares about nothing more than the law, which he sees as the same thing as justice. He is loyal and hardworking to the extreme, and in his own harsh way, he is fair: he shows no leniency toward anyone, including himself.
Fantine: Hufflepuff. Fantine is practical, industrious, and tragically taken advantage of. As a young woman, all she wanted was to be happy and loved, and once she finds herself alone and desperate, her greatest wish is for her daughter to be safe and cared for. She is eager to do honest work and earn a living, and she saves most of what she makes to send to Cosette. When she loses her job, it’s the thought of providing for her daughter that leads her to sell, first her hair, then her teeth, and finally, her body.
The Thenardiers: Slytherin. The Thenardiers are the true evil of Les Miserables, no matter how much the musical might try to make them into comic relief. We first meet them when they are innkeepers ripping off every customer who comes to their inn, later as part of a gang in Paris, and finally, attempting to blackmail Marius and profiting from the deaths at the barricade. But each time we see them, they are greedy, selfish, and conniving. They are Slytherins in the worst way possible.