The 30-year-old has signed for Rhinos after two seasons with Huddersfield Giants.
A Man of Steel nominee in 2020, the half-back previously played for Gold Coast Titans and Canberra Raiders in the NRL and reckons he is joining “the biggest club in Super League”.
Sezer said: “I hope I can be part of a successful couple of years 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.
“A lot of the boys who have been at the club in the past cannot speak highly enough about the Rhinos. It will be a good environment for me to play my best.”
He added: “Leeds sells itself to you because of the size of the club.
“Back home, I used to watch Leeds when I was growing up, I am really excited to be joining the club and can’t wait to be a part of it.”
Rhinos coach Richard Agar hailed Sezer as “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”.
He said: “I know 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.”
Director of rugby Kevin Sinfield added: “We are delighted to have signed Aidan. With Rob Lui leaving us at the end of the season, strengthening our half-back options was a priority 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 year.”