The back-rower has signed a two-year deal for 2015 and 2016, with an option to extend the contract by another year.
The 27-year-old Tongan international, who was born in Sydney, has previously played for Melbourne Storm and St George-Illawarra Dragons.
“I had offers from many different clubs but once I spoke to Mike Rush and Nathan Brown, and had the chance to view Langtree Park and the training facilities, I felt it was the right fit for me,” said the player.
“Saints have a nice culture and environment and that attracted me to sign.
“I played against Saints not too long ago and liked the feeling of the place even though we lost. The crowd were very vocal and it felt like somewhere I would like to be.
“I’m looking forward to playing in front of those fans and getting them on my side.”
“I want to come there, play my own game and hopefully the fans will embrace me.”
Saints head coach Nathan Brown belieces that Vea is similar in playing style to Willie Manu.
“Atelea had a lot of interest throughout Super League and we are pleased he decided to join the Saints.
“He is a similar player to Willie Manu in the fact he is quite robust, has good feet and speed and can use the ball well.
“He has the ability to play before and in the line and will be a great addition to our squad.”