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.
"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."
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