The Vilnius City Council adopted the decision under a fast-track procedure on Wednesday.
Vilnius Mayor Remigijus Šimašius had proposed to name the public garden under Russian democrats, but backed down from his position after meeting with prominent Russian opposition activists who visited Vilnius and with Russian nationals granted asylum in Lithuania.
The mayor said that the naming of the place after Nemtsov would be a sign of respect for the entire Russian democratic movement.
"When we name that space after Boris Nemtsov, it will be a sign of respect not only for this particular person who was a bright figure, a person with all his strengths and weaknesses, but who has also become a symbol of the present-day democratic movement, of the present-day democratic resistance," he said during the council's meeting.
Vladimir Kara-Murza, a Russian opposition politician and journalist, said that he always felt Lithuania's support for Russian democrats.
"A person may be killed, but it is impossible to kill the memory of that person and the principles and values that person fought for," he told the council.
Šimašius said that the Lithuanian Foreign Ministry supported the idea of naming the public garden after Nemtsov.
According to the mayor, Vilnius will become the second city to immortalize the murdered Russian opposition activist. A part of a street near the Russian embassy in Washington, D.C. has been named after him.
It is planned that the public garden in Latvių Street will have various artistic elements and benches named after democrats.
Nemtsov was shot dead on a bridge near the Kremlin on February 27, 2015. The opposition leader visited Lithuania many times and was one of the most active supporters of Lithuanians during the Soviet forces' bloody attack on protesters in Vilnius on January 13, 1991 and afterwards.