His radical agenda scares even many Europeans who have railed against austerity. And if he's given the power to carry it out, Greece may soon find itself kicked out of the euro common currency.
Opinion polls now put his Syriza party, which long struggled to win seats in Parliament, in a dead heat with the once powerful center-right New Democracy. The election is Sunday.
Greeks deserted mainstream parties in May 6 inconclusive elections after the country sank into a government-debt crisis that forced draconian spending cuts. Even low-income pensioners and minimum wage-earners have been forced to make sacrifices.
Syriza came in second to the conservatives in the May 6 elections that failed to produce a government, winning nearly 17 percent of the vote and increasing its support four-fold.
"The rotten and reliant establishment is making its last stand. Their dominance is ending after they looted the country and saddled it with debt," Tsipras said at a recent campaign appearance.
Friends describe him as down-to-earth and committed to change. He is Greece's first major political leader to be born after the fall of the country's 1967-74 military dictatorship, which ended decades of political turmoil. He grew up in an era of unprecedented political freedom in Greece, without having experienced any of the harsh polarization between left and right that marked the country since the mid-1930s.
"He has played a big role in the party's [success], mainly because he's a politician who does not keep his distance from people," ranking Syriza member Sofia Sakorafa told the AP.
Sakorafa, a longtime javelin world record holder before going into politics, said she was impressed by Tsipras' ability reach out to voters.
"He can talk to people, and he is genuine. He wins them over with the truth as he believes it."
Rarely seen wearing a tie, Tsipras has broken the mold of the Greek career politician. Unlike many of them, he isn't linked to one of the country's powerful families, and during the crisis he hasn't been seen as being out of touch.
He has been riding high on a wave of anti-austerity sentiment that has swept the country as deep spending cuts have eaten into health care, salaries, and pensions, sent the unemployment rate soaring and forced tens of thousands of businesses to shut down since late 2009.
Despite two international rescue loan packages, Greece has been unable to pull itself out of its debt crisis, leading the heads of all the main political parties to argue for some form of renegotiation to the terms. But it is Tsipras who has the most radical approach, saying that simply extending loan repayment times or slightly tweaking targets will not work. He wants the terms cancelled.