Sam Riley was Salles' first choice to play Sal Paradise, the wide-eyed writer who represent's Kerouac's fictionalised self in the novel. Riley had reconciled himself to missing out on the part when Pathé pulled the plug, but couldn't believe a second chance had presented itself when Salles came calling once more. "I was going to do it two and a half years ago," he told Collider, "and then it ran out of money, so I thought I was just on the list of other actors that nearly played the role, and I was quite happy with that, to be honest, because it’s a great list. I wouldn’t have had to go through the humiliation of getting it wrong."

As it turned out, the part was still his, and Riley threw himself into an intensive process of transformation. "That was probably the most I’ve had to prepare for something," he explains, "because there’s an awful lot of expectation riding on that. Preparation wise, I’m a pasty, very skinny, Englishman, and I was going to be playing a sporty American, so the first thing I had to do was get a personal trainer and whip myself up into shape in a very short amount of time. I had dialect coaching every day, for two months before shooting and throughout as well. I learned to speak French-Canadian with a Quebecois accent, and I learned how to use a typewriter. Fortunately, I can smoke, which he was very good at, as well."