The 28-year-old, from French side Beziers, is part of director of rugby Chris Sterling’s recruitment drive as Carnegie battle to pull away from the foot of the Championship table and build a side capable of competing for promotion to the Premiership in 2019/20.
Niko, who is originally from Wellington in New Zealand and of Samoan descent, joined NRL outfit New Zealand Warriors in 2008 before moving to Melbourne Storm three years after that.
He switched codes as part of the Australian national sevens squad before moving to France to play with Section Paloise, Albi and Beziers and has agreed a contract with Carnegie until the end of next season.
He joins recent signings Fa’atiga Lemalu (Auckland), Cian Romaine (North Harbour), Tom Hill (Otago), Myles Thoroughgood (Northland), Nic Mayhew (North Harbour), Antonio Kiri Kiri (Manawatu), Jade Te Rure (Manawatu) and Craig Mitchell (Newcastle Falcons) in Carnegie’s squad, alongside loan players Jacob Umaga (Wasps), Will Britton (Bath) and Sam Nixon (Bath).
Defiant Ralph Hasenhuttl offers Leeds United apology after Southampton score draw
Injury crisis deepens for Leeds United's Premier League rivals as another star limps off
Leeds United dealt Patrick Bamford injury blow at Southampton with fellow striker already out
Jesse Marsch reveals extent of Patrick Bamford and Joe Gelhardt's Leeds United injuries
Leeds United and Crystal Palace ‘monitoring’ £30m striker, Whites could be ‘offered’ Aston Villa star
Stirling said: “Elijah is a very talented player who will add real strike to our backline. He is an exciting player I am sure Yorkshire Carnegie fans will enjoy watching and I am looking forward to him linking up with the group.”