The 23-year-old, who can play lock, flanker or number eight, made 19 appearances in his first spell at London Irish after graduating from the Exiles academy.
London Irish director of rugby Brian Smith said: "Jon is a player I have worked with before and he possesses a huge amount of potential which has been on show throughout the last season at Bedford Blues.
"He deserves the chance to be back and I know he will continue to work as hard as ever."
Another ex-Premiership player has returned to their old club as
Tu'ipulotu, the former Junior All Black, is the Falcons' fourth signing this week following the arrivals of Rory Lawson, Carlo del Fava and Scott MacLeod.
Newcastle's immediate future remains uncertain as they wait for the outcome of the Championship final to discover whether they will be relegated.
But Tu'ipulotu is excited by the prospect of playing under new director of rugby Dean Richards.
"I am truly grateful for the opportunity to join the Falcons again," Tu'ipulotu told the Falcons' official website.
"When I initially left the Falcons for Japan it was a very hard decision for me and my family to make.
"During my time away Semore Kurdi has taken over the club, and it is great to see the progress that has been made under his leadership, especially with the appointment of Dean Richards as director of rugby.
"I am looking forward to being part of a team that strives to perform to the expectations of its loyal supporters."
Newcastle say that more signings are set to be announced in the coming days.