The prosecution had demanded a 12-year prison sentence for Khamiyev.
His accomplice, Umar Batukayev, who was found guilty of using forged documents and illegally buying and storing arms, received a five-year prison sentence.
A third suspect, Ruslan Musayev, was acquitted of all charges.
Khamiyev was convicted after a jury handed down a guilty verdict. The jury found only Khamiyev guilty of planning to kill Kadyrov.
Chechnen residents Khamiyev, Batukayev and Musayev were accused of being a part of terrorist group which planned to kill the president by detonating a car bomb near the Chechen representative office in downtown Moscow.
The car in question was found packed with explosives in southern Moscow on May 8, 2008.