"Leonid Nevzlin and Alexei Pichugin [a Yukos security official currently serving a life sentence] conspired with other unidentified people from the company's management to commit crimes," the court ruling said.
"Nevzlin poses a serious danger to society and must therefore be sentenced to life imprisonment," the verdict said.
Investigators say that between 1998 and 2002, members of an organized criminal group led by Nevzlin murdered, among others, the mayor of Nefteyugansk, where Yukos's main production unit was based, and businesswoman Valentina Korneyeva, who stood in the way of the oil giant's interests.
Nevzlin, who fled to Israel in 2003, has repeatedly denied the charges as politically motivated. The businessman's defense lawyers said they would appeal the ruling.
The court also ordered Nevzlin to pay over 5.5 million rubles ($235,000) in compensation to the victims and their families.
A state prosecutor said Russia could again demand the convict's extradition from Israel.
Previous requests were denied by Israel, which demanded more evidence of Nevzlin's guilt. The former major Yukos shareholder now holds Israeli citizenship.
State Prosecutor Alexander Koblyakov also said Nevzlin could serve the sentence in Israel.
"Russia and Israel have an agreement that allows for a Russian court verdict to be implemented by the Israeli judiciary," Koblyakov said.
A spokeswoman for Nevzlin said the ruling would not influence the businessman's life in Israel.
"Leonid Nevzlin has always relied on Israel's independent judiciary system... We have no doubt whatsoever that the Moscow City Court's decision will not influence Nevzlin's life in Israel in any way," Irina Dolgina said.
Once Russia's largest oil producer, Yukos collapsed after charges of tax evasion led to the company being broken up and sold off to meet debts. The bulk of the company's assets were bought up by state-run oil company Rosneft.
Nevzlin was a close adviser to Yukos founder Mikhail Khodorkovsky, who is currently serving an eight-year prison term for tax evasion and fraud in East Siberia. Khodorkovsky said his imprisonment in 2005 was punishment for his political ambitions and part of the Kremlin's drive to regain control of lucrative energy assets.
The widow of the late mayor of Nefteyugansk has repeatedly accused Khordokovsky of being involved in her husband's death. Before his murder, Vladimir Petukhov had been on a hunger strike demanding that the chairmen of municipal and district tax offices be dismissed from their positions and a criminal case against Yukos be filed on counts of tax evasion.
"The company had evaded local tax payments and hid its earnings from the public. Khodorkovsky managed to solve the problems through bribing important officials. The local budget and survival of the town completely depended on the tax revenues from Yukos. The town was left with no revenues and no means to survive," Farida Islamova said earlier.
She has also filed a $23.7 million suit against Nevzlin. She is claiming the money as compensation for her husband's death.
Petukhov's murder took place on Khodorkovsky's birthday, and soon after the shooting, local residents took to the streets, attempting to storm the local office of Yukos.
