The 27-year-old Tongan international joins them for the 2015 and 2016 seasons with an ‘option’ for the following season.
Vea said: “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. 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.”
London Broncos head coach Joey Grima said: “I’ve been liaising with Mike Rush and Nathan Brown and while we’re disappointed to be losing a player of Tils’s ability and professionalism, I would never stop anyone wanting to play Super League, given where we are at the moment.
“Tils’s has been an ultimate professional to me and personal friend. He accepted my invitation by coming over to play for the London Broncos and I wish him and his partner all the best for St Helens. I know the type of person St Helens are going to get and they couldn’t have picked anyone better than him.”
Saints head coach Nathan Brown added: “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.”