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.
Ulster number eight Nick Williams hit with eight-week ban for striking opponent
"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."
Bevington extends Ospreys stay
Former Red Roses star Alphonsi hails grassroots rugby experience as key to decorated career