The 29-year-old has made over 200 appearances for the Exiles but has decided to join former England lock Nick Kennedy in leaving the club this summer.
Worcester head coach Richard Hill said: "Paul is a hugely competitive, positive and enthusiastic player who has a fantastic attitude. He has huge drive to win at absolutely everything he does.
"He is a scrum-half who is lively around the park, knows how to control a game and puts his body on the line for the good of the team. He is a great character to have on the field and I know his enthusiasm will be infectious and will impact on those around him.
"We are determined to only bring people to the Warriors who will give 100 percent in every game they play and will improve our squad. Paul will do just that and has the work ethic and winning mentality to push the club forward."
Hodgson, who has won nine England caps and is currently a member of the Saxons squad, vowed to give his all to help London Irish reach the Aviva Premiership play-offs.
"I am excited by the rest of the season at London Irish and totally focused on helping the team move forward in the Aviva Premiership and make the end of season play-offs," he said.
"Worcester Warriors are an ambitious club with a strong coaching set-up and really developing playing squad.
"After meeting with Richard Hill I truly understood the aspirations of the club and I'm looking forward to playing my part in that development.
"I have thoroughly enjoyed my eight years at London Irish and I have been lucky enough to play with some fantastic team-mates and under a great management team. The support from the fans has always been amazing."
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The entire All Blacks apparel line has been updated for 2013/14. Check out the New Zealand All Blacks polo.
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