The 23-year old second row, who signed a new deal with the Ospreys earlier this year, will link up with his new colleagues at Wales Capital Region next week to prepare for the coming season.
He is the third addition to the first team playing squad in recent days, following the signings of Dmitri Arhip, also from the Ospreys and Jason Harries from Edinburgh.
Thornton saw his game time limited last season, injury restricting him to just four appearances, and following discussions between both regions and national team management, it was agreed that the former Wales Under-20s captain will make the temporary move up the M4 to allow him the best opportunity to get more game time and to assist his international ambitions going into a Rugby World Cup year.
Speaking about the move, Thornton said:
“I need to be playing rugby and Cardiff need a line out forward so this is a great outcome for everyone. It’s a good move for me in the circumstances and I’m looking forward to meeting the rest of the squad next week and preparing for an important season.
“I’m grateful to the Ospreys for supporting me like this and also to Cardiff Blues for giving me the opportunity.”
Thornton reported to Cardiff Blues training base today for testing ahead of the official start of pre-season on Monday.
Cardiff Blues Head Coach, John Mulvihill, commented:
“It’s great to welcome a player of Rory’s calibre to the Cardiff Blues.
“I have met him a few times now and I’ve been impressed with his desire to play international rugby again. He will get his opportunity to do this playing at the Cardiff Blues.
“The support and cooperation by the WRU, Cardiff Blues and the Ospreys shows Welsh rugby is heading down a path where their best players will get the opportunity to play every week at the highest level. This collective mindset will ensure strength and depth at a national level going forward.
“From a Cardiff Blues perspective, it is important that we have strength in depth in the position and Rory is exactly the right type of lock to add to what we already have.”
Allen Clarke, Ospreys Head Coach, said:
“The decision to allow Rory to go to Cardiff Blues on loan has been made in his best interests, with international ambitions in mind.
“A talented young rugby player like Rory will benefit from playing regular rugby, he has ambitions of going to the World Cup, and second row is a position where we have a number of options available. I want him to go to Cardiff and shine, knowing that we will welcome him back next year.
“It’s important for Welsh rugby that we work collectively to ensure the best outcome for individual players, regions and national team alike”