At 6ft 4in and 108kgs, the 23-year-old from County Meath is a physical presence with the ability to play at both inside and outside centre.
Fergus Mulchrone, who is over 6ft and weighs close to 100kgs, can play at outside centre, wing and full-back and has previously played for Sale Sharks. He rates scoring two tries for Sale Sharks against London Irish as his rugby highlight.
London Irish director of rugby Brian Smith said: "Eamonn and Fergus are both big talented outside backs and with their Irish heritage they're a great fit for our club.
"Eamonn has made a name for himself in the Leinster Academy and Fergus did the same at Sale. Both players have great attitudes and I expect them to put pressure on the matchday squad."