The 26-year old, a Grand Final winner with Saints, will join up with the Black & Whites for the 2020 campaign, bringing to end an eight-year spell with the Merseyside club.
Swift becomes Lee Radford’s second signing ahead of the 2020 Betfred Super League campaign, following last week’s announcement that Salford back-rower Josh Jones will link up with the Airlie Birds next year.
Like Jones, Swift was part of the St Helens squad that won the Super League Grand Final in 2014, as well as being part of the squad that won the League Leaders Shield last season.
He has maintained an impressive try-scoring record throughout his career, crossing for 99 tries in 141 career appearances, including 86 tries for St Helens.
Swift made his Super League debut in 2012 and he has nine career hat-tricks to his name, including in his league debut against Widnes.
Swift said: “I’m buzzing - I am over the moon! I can’t wait to get started and rip into the 2020 season with the boys.”
“Coming from a rugby town into another one, I’m excited to see what the fans give.
“Meeting Lee [Radford], he’s a really good coach and humble bloke. The vision he has for the team in the next couple of years is really exciting.
“When I come over to Hull next season I can get the chance to play regularly and that’s an opportunity I will take with both hands because I want to get over the whitewash and score some tries.”
Swift has scored four tries in three appearances this season after a period on the sidelines through injury, whilst also facing stiff competition for a wing spot with the emergence of youngster Regan Grace and Golden Boot winner Tommy Makinson.
However, his stats back up why Hull have swooped to secure the services of the experienced winger, who is known for his hard work and carries, as well as his space.
This season alone. Swift is averaging 145 metres, 17 carries and 5 tackle busts per game, which have been consistently high figures during his time in Super League.
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 back field 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.
“Adam has tasted success with his home town club before and hopefully he will taste some more in a Black & White jersey.
“I have been impressed with how Adam has come across during negotiations and I’m confident that he will become a valuable member of the squad.”