The 21-year-old has been given a full-time contract with the Broncos after impressing during a one-month trial.
"It's a massive challenge for me and I'm dying to get some games under my belt and press for first-team rugby," said Hurst. "It's what every rugby player wants to do and I'm here to take my chance."
London coach Tony Rea said: "He's come down and been given a trial and shown everything there athletically. We've thrown him some challenges and he's met them all."
The Broncos have yet to make a decision on the future of Wigan's John O'Donnell, who joined them at the same time as Hurst and will remain at the club on trial until the end of February.
"I want to see him through the trials and team sessions," added Rea. "We think he's shown some good things, we just want to have a look at him in the games."