Jones, 20, will move to the Arms Park for next season.
The Wales Under-20 international was selected for last year's Junior World Championship in South Africa.
"Ieuan has been a successful member of the Wales Under-20 set-up and is a real talent in the regional game," Blues rugby director Phil Davies said.
RaboDirect Pro12
Ulster number eight Nick Williams hit with eight-week ban for striking opponent
01/04/2015 AT 16:10
"He is a strong, young number eight and big ball carrier who will add both talent and depth to our squad as we look to next year and beyond."
RaboDirect Pro12
Bevington extends Ospreys stay
04/03/2014 AT 09:18
Rugby
Former Red Roses star Alphonsi hails grassroots rugby experience as key to decorated career
19/06/2021 AT 16:29