Galina Starovoitova, 52, was shot dead in the stairwell of her home in central St. Petersburg, Russia's second city, in November 1998.
Vyacheslav Lelyalin will serve his sentence in a high-security prison for helping to arrange the shooting of the State Duma deputy. He was detained in 2004 and faced charges of tapping telephone conversations and attempted murder of a state or public figure. He was found guilty on all counts last Friday.
The other defendant in the trial, Pavel Stekhnovsky, was sentenced to two years but released because the statue of limitations for his offense had run out.
A jury decided that the lawmaker's killing was not politically motivated. Starovoitova, the leader of the Democratic Russia party, was the only woman to run for the Russian presidency in the 1996 election and was considering joining the presidential race in 2000 at the time of her death.
The MP served as an ethnic advisor to President Boris Yeltsin in the early 1990s, was a human rights champion and worked with prominent human rights advocate Andrei Sakharov. She was known as an uncompromising politician.
Stekhnovsky was found guilty only of obtaining a weapon but cleared of murder charges. He was arrested in Belgium in 2004 and extradited to Russia to face charges of involvement in obtaining weapons, attempted murder of a state or public figure and a terrorist attack.
Two other men, intelligence officer Yury Kolchin and Vitaly Akishin, were sentenced in July 2005 to 20 and 23 and a half years in prison, respectively, for organizing the murder of Starovoitova.