Carrying Georgian and Ukrainian flags and placards that read “Stop Putin!”, the protesters gathered on the city’s main thoroughfare on Saturday, following the call of the former president Mikheil Saakashvili’s United National Movement party (UNM).
Saakashvili addressed the rally by video link from Kiev as the cheering crowd chanted his name.
“Let’s show Georgia’s government that the nation is united against the serious threat to its independence, its future,” he said.
Saakashvili’s UNM party has accused the ruling Georgian Dream coalition government of not confronting what it claims is Russia’s creeping annexation of Abkhazia and South Ossetia.
Backed by the Kremlin, the two regions broke away from Georgia after civil wars in the 1990s following the break-up of the Soviet Union.
Moscow officially recognised their independence after fighting a five-day war with Georgia in August 2008.
After that war, Moscow stationed thousands of troops in the two separatist statelets in a move condemned by Tbilisi and its Western allies as an illegal occupation.
Russia is already at loggerheads with the West after its annexation of the Crimean peninsula from Ukraine in March and its support for separatist fighters in the former Soviet country’s eastern belt.
Georgian Dream, assembled by former prime minister and billionaire tycoon Bidzina Ivanishvili, came to power in 2012 and ended a decade-long rule of staunchly pro-Western Saakashvili and his UNM party.
Accused by prosecutors of abuse of power, Saakashvili lives in a self-imposed exile in the United States.