The utility forward played 42 times for the Saints since making his debut against Leeds Rhinos in 2014.
Savelio joined the Saints from Latchford Albion and makes the move to gain more game time, at his own request, as he continues his development in the game.
The loan agreement has no recall, but Savelio cannot play against the Saints in the Super 8s.
Savelio, 21, is looking forward to working under Daryl Powell and can’t wait to get straight in to training.
Savelio said: “I’m really excited to be joining the Tigers for the rest of this season. I have a lot of respect for Daryl Powell and the way he coaches and I’m looking forward to getting straight in to training.”
Tigers head coach Daryl Powell said: “Andre Savelio is an outstanding young player who will now replace Danny Tickle in our squad for the rest of the season.
“Andre has always caused us trouble when we have played against him in the past and I’m sure he will fit neatly into the way that we play. I would like to take this opportunity to welcome him to the club.”
Castleford chief executive Steve Gill said: “After letting Danny Tickle go we knew Andre was available and we moved quickly to bring him in. He’ll be a great addition to our team for the Super 8’s and I look forward to seeing him in a Tigers shirt.”