Antonsson scored 22 goals in 40 league games for Kalmar after signing from Halmstads in January 2015.
The 25-year-old is Leeds head coach Garry Monk's first signing since replacing Steve Evans on 2 June.
"He scores goals, has great movement and he has the mentality to be able to adapt to this league," Monk said.
"The club has watched a lot of him, I've watched a lot of him and I felt he'd be a good fit for Leeds United."
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Championship club Leeds United have signed striker Marcus Antonsson from Swedish top-flight side Kalmar on a three-year deal for an undisclosed fee.