29th May 2019, 19:53 | Hull
The 26-year-old will make the move to the KCOM Stadium at the end of the season on a two-year contract after opting to end an eight-year spell with Saints.
With Salford Red Devils second rower Josh Jones already on board for next season, it means Hull will have two members of St Helens’ Grand Final-winning team of 2014 in their ranks.
Swift has scored 86 tries in 126 appearances for St Helens after making his debut in 2012 but has been restricted to just three matches so far this year.
Hull coach Lee Radford said: “Adam is a really good addition to the squad because it’s so hard to come by available English players of his calibre.
“He’s got a great try-scoring ratio but it’s his work from backfield which has really impressed me.
“He has notoriously caused us problems in the past so it will be great to have him doing that sort of stuff on our side.”
Swift said: “It was a really tough decision to make, being a homegrown lad and moving away, but it’s the right decision for me and I’m really looking forward to it and to the challenge ahead.”
Saints coach Justin Holbrook said: “I can completely understand Adam’s decision to move on.
“He is a Super League player and has, unfortunately, had limited opportunities in his position in recent times.
“Selfishly, I would have loved to have kept him. He is a great guy and it’s a shame that someone with such close affinity to the club will be moving on.
“I wish him all the best for the future.”