Renzi held talks with President Vladimir Putin in a visit that also focused on the conflict in Ukraine and Russia's chilly relations with the European Union over its backing of separatist rebels in eastern Ukraine.
Renzi began his visit by laying flowers on a bridge where opposition politician and former deputy prime minister Boris Nemtsov was gunned down near the Kremlin on Friday night.
Then he raised one of his country's most pressing concerns with the Russian strongman: the chaos in Libya which has seen thousands of migrants flee to Italy and also sparked fears of a new stronghold for jihadists to launch attacks on Europe.
"We need a strong international response" to the crisis in Libya, Renzi said in comments published on the Russian presidency's website.
The Tass news agency quoted Renzi as calling for joint efforts to fend off "terrorism and religious fanaticism."
He said Russia's role in the UN Security Council and its relations with Egypt could provide crucial help in finding a solution to the Libyan crisis.
"I am confident that the Russian Federation may play a decisive role in resolving the problem," Renzi said.
Putin said he supported UN mediation efforts and called for a peaceful resolution of the crisis in Libya, which has been wracked by conflict since the overthrow of dictator Moamer Kadhafi in a 2011 Nato-backed uprising.
Rival governments and powerful militias are battling for control of key cities and the country's vast oil riches, and the chaos has provided fertile ground for the Islamic State group.
"We had a detailed discussion of the terrorist threat coming from the Middle East and North Africa, particularly the sharp deterioration of the situation in direct proximity to Italy - in Libya," said Putin.
Renzi's visit to Russia came a day after he held talks in Kiev with Ukraine's President Petro Poroshenko.
Italy and Russia have long had strong ties, but like the rest of the European Union, Rome slapped sanctions on Moscow for its role in the Ukrainian crisis.
When he announced his visit Renzi said he wanted to relay the message that "if Russia returns to the international table we will all be more at ease."
"We, of course, exchanged views on the Ukrainian crisis," said Putin, adding Renzi had "made valuable proposals regarding what could be done to achieve a settlement. The situation there, as we all know, remains complicated. At least combat action has been stopped, people are not dying and towns are not being destroyed."