The 24-year-old utility back has signed for Connacht from Wellington Norths on a two-year deal.
The westerners' incoming head coach Pat Lam, who has worked with So'oialo in Samoa, said: "James is a superb utility back who can play all positions but half-back. He can kick goals from up to 60 metres out and I'm sure with the Galway wind, we will see him kick from even further out.
"To have someone in our squad with so much versatility and who can kick goals from that distance is a real weapon in our armoury.
"James will join us for the pre-season straight from his summer duties with Samoa and I'm looking forward to catching up with him then."
Following Leinster's Amlin Challenge Cup win at the weekend, Connacht have secured a place in the Heineken Cup for a third consecutive year.
"We will be competing in the Heineken Cup again next season and that is fantastic. We have seen the positive impact the competition has had on the community over the last two years," added Lam.
"To be playing against the best teams in the most elite rugby competition is where we want to be and this is how we grow and build on the work that has been done over the last number of years.
"Personally, I loved being part of the Heineken Cup as a player and I am now very excited about my involvement as a coach for the first time."
Connacht Chief Executive Tom Sears added: "James is an international class player and someone Pat knows very well and has coached previously.
"From the outset Pat was very keen to get James to Connacht and identified him as a player who could be a real asset to us, so we are delighted that we have been able to bring him in.
"We have now filled all our non-Irish eligible positions and have a full quota of special project players with the recent signing of Jake Heenan.
"We are very excited about the quality and potential of the players we have been able to add to the squad and with the prospect of another season of Heineken Cup rugby to look forward to, next season promises to be a hugely exciting one."
CONNACHT - 2013/14 INCOMING PLAYERS:
Hookers - Sean Henry; James Rael; David Heffernan (Connacht Academy)
Second rows - Craig Clarke, Aly Muldowney; Daniel Qualter (Connacht Academy)
Back rowers - Jake Heenan; Aaron Conneely (Connacht Academy)
Out-half - Craig Ronaldson
Winger - Fionn Carr
Utility back - James So'oialo