The other defendants received sentences of between eight and 35 years' imprisonment.
Most of the 12 people who were convicted of being involved in the conspiracy were members of the Zemun mafia gang, and many fought as paramilitaries in the Bosnia, Croatia and Kosovo wars.
|Protesters said the trial failed to establish |
who really ordered the murder [Reuters]
Ulemek was the former head of the elite Red Berets paramilitary unit set up by Slobodan Milosevic, the former Serbian president who died during his war crimes trial in The Hague in March 2006.
Djindjic, a pro-Western reformer, took power after Milosevic was forced from power in October 2000.
Nationalists condemned him as a traitor in 2001 for extraditing the former president to the war crimes tribunal.
The indictment said the defendants killed Djindjic in an attempt to bring hardliners back to power, to avoid being sent to The Hague, and because they feared a crackdown on organised crime.
"It was not an ordinary murder, it was a political murder with an aim to destabilise the state," Mesarevic said after the verdict.
Ulemek is already serving a 40-year sentence for the murder of Ivan Stambolic, a former Serbian president, in 2000, as well as a 15-year term for the attempted assassination of Vuk Draskovic, an opponent of Milosevic.
Djindjic's supporters have criticised the trial, which lasted three and a half years and heard testimony from 150 witnesses, saying it failed to show who really ordered the assassination.