Roach, 20, becomes the Scorpions second non-Welsh qualified player and is the second Skolars player to move to South Wales this season, following on from Cardiff-born Curtis Cunningham.
The son of legendary ex-Australian International Front Rower and New South Wales State of Origin legend Steve Roach, Roach has played reserve grade for Canterbury and Wests in Australia and has an Irish passport.
He goes straight in to the squad to face Blackpool on Monday, and coach Anthony Seibold knows it will be a tough challenge.
He said: “Blackpool are undefeated so far this season in Co-operative Championship One and are also through to the next round of the Carnegie Challenge Cup where they have a super tie against Leeds Rhinos. They could not have asked for anymore from their squad so far this season.
“I am looking forward to us being able to test ourselves against another of the leading sides in this division. We are in the middle of a really tough run of games but we have shown improvement each week since our big defeat against Hunslet a couple of weeks back, without being able to clinch a result. We know we will need to be at the top of our game this Monday.”