Sezer joins the Tigers on a one-year deal and looks likely to partner fellow recruit Jayden Sullivan in the halves as Wests hope to chart a course up the ladder under the rookie coach.
Canberra's halfback in the 2019 grand final loss, Sezer returns to the NRL after four seasons in the English Super League.
He has 155 games of NRL experience as well as two games for the Indigenous All Stars and one for NSW City.
"We are very excited to have a player with Aidan's experience and calibre to add to what we're building for our future," Marshall said.
"His experience will complement our youth and he'll help mentor our younger players, particularly in our spine."
Sezer's arrival comes as the Tigers prepare to lose long-term halfback Luke Brooks to Manly and first-choice five-eighth Adam Doueihi to a knee injury for the majority of next year.
The Tigers have been hampered by their instability in the halves this season, which looks likely to end with a second consecutive wooden spoon.
Brandon Wakeham, Daine Laurie, Starford To'a, Api Koroisau and Will Smith have all started in the halves as the club tried to combat injuries to Doueihi and Brooks.
Wakeham and Smith are yet to re-sign beyond this season, while Laurie is already moving back to former club Penrith.
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