The purpose of this study was to develop a kinematic model of a gear-driven rotary planting mechanism for a self-propelled onion transplanter. The kinematic model was simulated using a commercial mechanical design and a simulation software package, and was validated through an on-site performance test. Torque and acceleration sensors were installed with an input power shaft and hopper jaws, respectively. Through kinematic analysis and simulation, the appropriate length combinations for primary, connecting, and planting arm were determined as 90, 70, and 190 mm, respectively. The diameters of the driver, driven, and idler gears in the primary arm were 56, 48, and 28 mm, respectively. For the secondary link, the diameters of the driver, idler, and driven gears were 28, 28, and 56 mm, respectively. The length of the planting hopper was selected as 190 mm and remained constant during the kinematic analysis. The maximum magnitude of the velocity and acceleration of the planting mechanism were determined as 1032 mm/s and 6501 mm/s2, respectively. The power consumption was measured as 35.4 W at 60 rpm. The single- and double-unit assembly of the studied rotary planting mechanism can transplant 60 and 120 seedlings/min, respectively.