Today he has catapulted into contention for his party's nomination, suddenly omnipresent despite not yet officially declaring his candidacy.
And he's blazing his own path, with a balance of calm and confidence, problem solving and intellectual ambition that has impressed at campaign stops in early voting states like Iowa and South Carolina.
The Buttigieg buzz has mushroomed quickly.
"This is something real, this is not flash," former Iowa Democratic Party chair Sue Dvorsky told AFP, as she highlighted his mayoral successes and his astute discussion of issues.
He draws sharp contrasts with Trump on multiple fronts including age, government experience, military service, campaign style, and "intellectual curiosity," she added.
"Every single thing about him is in diametric opposition" to the president, she said.
Buttigieg is relishing his breakout moment, fuelled by a star turn headlining a recent town hall that saw his national profile skyrocket.
Bookish and smart, he refutes the charge that he's too young and inexperienced to compete in the diverse Democratic field, or against Trump himself.
"I have more years of government experience under my belt than the president... and more military experience than anybody to walk into that office on day one since George H.W. Bush," he said at the event, broadcast by CNN.
"So I get that I'm the young guy in the conversation, but I would say experience is what qualifies me to have a seat at this table."
In Iowa, Buttigieg surged from one percent support to 11 percent and third place in Emerson Polling's survey released Sunday, behind former vice president Joe Biden and Senator Bernie Sanders and ahead of more prominent candidates like senators Kamala Harris and Elizabeth Warren.
He has proved he can raise all-important campaign donations, pulling in $600,000 in the 24 hours after his town hall.
Source: The City of South Bend
The man many people call "Mayor Pete" grew up in South Bend, a once thriving city whose economy imploded when auto giants like Studebaker closed their factories in the 1950s and 60s.
The community has clawed its way back, and solution-oriented Buttigieg has been credited with revitalizing its downtown.
In 2016, as Hillary Clinton battled Trump, Buttigieg noticed a "fatal lack of enthusiasm" among working-class voters in the heartland when it came to the Democratic message.
This cycle, his party must re-engage with disaffected Midwesterners who supported Trump, he said.
"Our whole message was 'Don't vote for him, because he's terrible.' And even though he is, that's not a message," warned Buttigieg on "The Breakfast Club" radio show in New York.
"I hate to say it, but he could absolutely win again if we aren't smart about this."
As mayor, Buttigieg worked -- and sometimes clashed -- with Indiana's then-governor Mike Pence, a religious conservative who is now vice president.
He leveled withering criticism at his fellow Hoosier at the town hall.
"How could he allow himself to become the cheerleader of the porn-star presidency?" Buttigieg said.
"Is it that he stopped believing in scripture when he started believing in Donald Trump?"
Buttigieg supports health care expansion to all Americans, initially through allowing people to buy into the federal Medicare program.
He believes in strong labor unions and opposes Trump's ban on transgender people serving in the military.
He wants the Electoral College scrapped, arguing it is undemocratic, and has suggested expanding the US Supreme Court to 15 justices.
The former Rhodes Scholar came out as gay while running for re-election -- and won with 80 percent of the vote. He is married to husband Chasten Glezman, a teacher.
As a lieutenant in the US Navy Reserves, Mayor Pete paused his official duties while serving seven months in Afghanistan as a counterintelligence officer.
He has positioned himself as a post-Trump unifier, and made a light-hearted offer to strike a "peace deal" between the LGBT community and Chick-fil-A, the fast-food chain which courted controversy over its conservative leanings.
"I do not approve of their politics, but I kind of approve of their chicken," Buttigieg quipped on the radio.
"Maybe, if nothing else, I can build that bridge."