The 19-year-old made his first team debut for the Rhinos in 2013 and he has six Super League games to his name.
He will be available for selection for the Broncos’ Good Friday game against Featherstone Rovers.
“Elliot comes highly recommended from Leeds and has come through a good system,” said London coach Andrew Henderson.
“I feel Elliot will add competition for places and some quality to our forward pack.
“He has the potential to have a strong career in the game and we hope he does a good job at this stage of his development with the London Broncos.
“It’s always difficult to bring in player over this tough Easter period and I’d like to thank Leeds Rhinos at this time for allowing Elliot to join us.”
The player himself is looking forward to being able to develop in a new environment in the capital.
“I’m really excited to be coming down to London, it’s a massive change of scenery but I’m going to learn a lot from being down here,” he said.
“It’s really good for my development to play with some great players down here and hopefully I’ll do a good job for London.
“I’ve not set any personal goals, I just want to do my best personally and for the boys. Joe Keyes has helped me out a lot as I knew him prior to coming down so he’s helped me settle in and it’s gone very smoothly.
“It’s very different from up North but I’m enjoying it.”