The 24-year-old former Wales Under 20 captain spent a highly successful season at the capital city region on loan from the Ospreys and made 20 appearances. That was enough for him to make a big enough impression to earn a new contract.
“I really enjoyed my first season, and it’s a great opportunity to continue my progress here. Cardiff Blues have shown big faith in me by offering me this permanent deal – it’s a huge thing for me,” said Thornton.
“I struggled a little bit at the start of last season coming off the back of a shoulder injury. It was about getting some confidence back and having a run of games under my belt.
“Towards the second half of the season I felt I was getting back into form. I’m excited to have an opportunity to kick on next season and build on that with the Blues.
“There’s big potential in this team and I find the way we’re playing really exciting, especially with the likes of Jarrod Evans at No 10 and with boys like Owen Lane, Aled Summerhill and the new signings out wide.
“The Ospreys obviously played a big role in my development and I’m thankful to the organisation for their support over the years. But now I’m really excited to start a new chapter and making this move is the best step for my career.”
The 6ft 7in tall Thornton made his senior Wales debut in the 19-17 victory over Samoa on the 2017 summer tour. That is his only cap to date, but he has been included in other squads by Warren Gatland.