“He can play in more than one position and his versatility will be a great fit in the side,” said Swansea head coach Vitor Matos.
“Elijah joins us after performing well in all aspects of our recruitment process, and after a brilliant performance at the World Cup and we are very happy to have him with us.”
Just joins fellow New Zealand international Marko Stamenic at Swansea.
He will also be reunited with summer signing Stephen Welsh, who spent last season on loan at Motherwell from Celtic.
Swansea City midfielder Ethan Galbraith said his calf injury is “all good” after being included in Northern Ireland’s squad for friendlies with Guinea and France.
Galbraith had not played since the friendly draw with Wales at the end of March, which came after Northern Ireland’s World Cup play-off defeat by Italy.
In April, Swansea boss Victor Matos said he would prefer the 24-year-old was rested for June’s international window, but Galbraith said he had conversations with his club manager and the medical team.
Having missed the remainder of Swansea’s Championship campaign, Galbraith said he had been “ticked off” by the club’s medical team to link up with Northern Ireland.
Northern Ireland face Guinea in Spain on Thursday before facing France in Les Bleus’ World Cup send-off in Lille on 8 June.
“I’m happy to able to come to camp”, Galbraith said.
“I spent six or seven weeks just with a physio, so that was quite long just training by myself but it is all good now.
“When you spend time off the pitch it’s obviously frustrating. So having these games is absolutely brilliant for everyone, but coming off the back of an injury, it’ll be good to get back out there.”
After an impressive first season at Swansea, where he has been deployed at right back as well as in midfield, Galbaith has been linked with a move to the Premier League, as well as Championship rivals Wrexham, but he says his focus is on his current club.
“It’s nice when you see people are saying that you are doing good things, but at the moment I’m a Swansea player and will just try and focus on Swansea.”