Walker recently completed a loan spell at Whitehaven, and will go straight into London coach Andrew Henderson‘s squad to face Bradford this weekend.
“Jonny will add size, aggression and experience to the pack,” Said Henderson.
“I’m really excited to have Jonny on board and his addition gives us much needed cover in the front row.”
Leigh Centurions head of rugby Derek Beaumont added: “With London being a full-time club it is less disruptive for him as he will be training continually rather than training at our club full-time and then spending part of the week at a part-time club.
“We will continue to monitor his progress during his time at London. As part of the agreement Jonny will not be able to feature in any game against Leigh Centurions during the loan period.
“This is always standard procedure when players go on loan to other clubs that they don’t play against their parent club.”