Nearly 3 years later, Sunday's constitutional referendum could send the youthful prime minister sliding back down the greasy pole of politics, temporarily at least.
Nearly three years later, Sunday's constitutional referendum could send the youthful prime minister sliding back down the greasy pole of politics, temporarily at least.
If, as the polls suggest they will, voters reject Renzi's plan to streamline parliament, the centre-left leader has said he will step down.
The self-styled outsider in a hurry to shake up Italy finds himself on the inside, a target for those who say he has not been quick enough in fixing long-standing problems.
Renzi was just 39 when he came to power via an internal party coup in February 2014.
With his penchant for retro sunglasses, open-necked shirts and jeans, the former mayor of Florence was hailed at the time as a premier for the smartphone generation.
But the breath of fresh air is now in danger of being blown away by rival young Turks from populist and far right opposition parties trying to force him out.
After 1,000 days in office, Renzi, now 41, boasted last month of having steered the economy out of recession, got Italians spending again and improved public finances.
He has also had significant political victories: a controversial Jobs Act passed, election rules rewritten and his candidate, Sergio Mattarella, installed as president.
All were seen as evidence of the deft touch of a political operator who learnt his trade in Machiavelli's home town in the age of social media.
As his Twitter follower numbers rose, so too did his international profile. Renzi was feted for his reform efforts by US President Barack Obama and German Chancellor Angela Merkel.
"Matteo has the right approach and it is beginning to show results," Obama said just before treating Renzi and his school teacher wife Agnese to the last official White House dinner of his administration in October.
But many Italian voters do not share Obama's optimism. As the recovery has struggled to gain traction -- leaving unemployment stubbornly high, particularly among young people -- Renzi's ratings have slipped.
The Jobs Act, which eased hiring and firing, made him business friends but alienated trade unions and the left.
A bullish style that was once seen as energetic has come to be viewed by some as high-handed, including by some grandees of his own party.
Former Prime Minister Massimo d'Alema, a fervent critic of Renzi's constitutional proposals, described his successor to the New York Times as a Twitter-obsessed "oaf".
The decline in Renzi's popularity is relative however. Polls suggest the Democratic Party, under his leadership, would top an election held tomorrow, albeit only just.
To some, Renzi is a ruthless schemer who stabbed party ally Enrico Letta in the back when he orchestrated his ouster from the premier's office in February 2014.
The move came only three months after Renzi had been elected leader of his party on the strength of his work in Florence, where he cut local taxes and tried to foster innovation.
Critics say his record of doing that at a national level is patchy, noting how he has avoided a fight over public sector pay and privileges.
Promised reforms of the education and judicial systems have yet to get underway and Renzi, a practising Catholic, largely stayed out of the battle as legislation on same-sex civil unions was watered down, denying gay couples equal adoption rights.
Born on January 11, 1975 in Florence, Renzi studied law and took his first steps in politics as a teenage campaign volunteer for future prime minister and European Commission chief Romano Prodi.
By 26 he was a full-time organiser for La Margherita (The Daisy), a short-lived centre-left party.
He was only 29 when he became the leader of the province of Florence in 2004, establishing a power base that enabled him to go on to become mayor in 2009 and prime minister five years later.
But for a brief spell in his early 20s working for the family advertising business, politics is all he has done and friends say he would be loath to give it up, despite his protestations to the contrary.
Even if has to make way as premier, he is not expected to give up the party leadership.