The 24-year-old England Knights player made his Giants debut in 2017 and has scored 47 tries.
McIntosh, who can also play full-back and centre, said: “I’m really happy the news is finally out there that I’m going to be playing in black and white next season.
"As soon as the opportunity came across and I had the discussions with the club, I knew it was the right opportunity for me and I’m so pleased that the deal has been done."
He added: “At this point in my career, I feel like it's a great move for me.
"I know there is a lot of hard work ahead to get the rewards I’m hoping for, but I’m determined to do that and repay the faith the club have put in me.
“I’ve come through the ranks at Huddersfield and been in the system for over a decade since I was 13.
"I’ve had a lot of opportunities there and worked hard, but I feel like it’s time for me to kick on now with a new challenge and reach my new goals at a great club like Hull with a good environment.
“I had a few options, with staying at Huddersfield being one of them.
“It wasn’t an easy decision to leave the club after so long, but having explored my options and weighed everything up with my family and friends, this felt like the right and natural fit for me.
“I came away from my meetings with Brett [Hodgson, Hull's coach] feeling really comfortable and excited for the challenge ahead.”
Hodgson described McIntosh as "a skillful, high-quality player who we’re really excited to be adding to our ranks next season".
He said: “His ability to cover a number of positions is a real bonus in terms of our depths across our outside-backs and - being a young British player on the rise, who is still relatively young in his career despite having played over 100 games already - he’ll make a great addition to the environment we’re building here.”
Hodgson stressed: "We needed to add some speed to the squad and that’s a quality he certainly possesses.
“Having spoken to him on several occasions, he’s at the stage of his career now where he is ready for a change to help him take that next step in his career.
"Coming to Hull will be a good challenge for him and being an England Knights representative shows the calibre of player we’re bringing in."