The 30-year-old Sezer, who was a runner-up for the Steve Prescott Man of Steel award in his first season in Super League in 2020, will link up with the Rhinos at the end of the year when his contract with the Giants runs out.
Leeds coach Richard Agar said: “Aidan is a top-class player and a skilful half-back who will help bring the best out of the exciting talents we have in our team.
“I know that he had attracted interest from other clubs, both here in Super League and the NRL, however I think it speaks volumes for his hunger and ambition that he wants to try and be part of a successful era at Emerald Headingley.”
Sezer made over 150 appearances in the NRL for Gold Coast Titans and Canberra before joining Huddersfield and was in the Combined Nations All Stars team that beat England last month.
Leeds director of rugby Kevin Sinfield said: “With Rob Lui leaving us at the end of the season, strengthening our half-back options was a priority for us and Aidan was someone we identified early on as a good fit for our style of play.
“He impressed everyone in Super League last season with Huddersfield and I think he will thrive in our environment from next season.”
Sezer, who is currently sidelined with an ankle injury sustained the All Stars game, said: “I am really excited about the move across to the Rhinos.
“In my opinion, the Rhinos are the biggest club in Super League and I hope I can be part of a successful couple of years in my time here.
“Leeds are known for their fan base and the enormity of the club and I am looking forward to experiencing that as a player.
“It will be a good environment for me to play my best. Leeds sells itself to you because of the size of the club.
“Back home, growing up I used to watch the Leeds side and I am really excited to be joining the club.”