London Breed became San Francisco’s 45th mayor on Wednesday, taking the oath of office on the steps of City Hall and capping a rise from nearby public housing to the city’s top elected post.

Breed addressed thousands of spectators, reminding the audience of her personal story and laying out her vision for the city's future.

"I stand at this podium today because a community believed in me," she said. "I am here in the hope that together we can build a San Francisco where the next generation of young people can go from public housing to the mayor's office."

The ceremony marked a return to power for Breed, the former Board of Supervisors president, who briefly served as acting mayor after the death of Mayor Ed Lee in December.

Breed began her remarks on Wednesday with a moment of silence in memory of Lee.

Breed's removal from leadership earlier this year (orchestrated by her progressive opponents on the board) was an opening salvo in a short but hostile race for mayor in which Breed edged the leading progressive candidate, former state Sen. Mark Leno.

The city’s ranked-choice voting system led to a razor-thin margin of victory for Breed, who declared victory after more than a week of vote-counting.

In her inauguration speech, Breed called on city leaders to unite in order to take on issues like housing and public safety.

"We can't let the politics of progressive and moderate get in the way of our ability to deliver for the people of San Francisco," Breed said.

Shoring up relations with her progressive opponents could be equal parts good faith and good politics, as Breed will have to pursue her agenda with a progressive majority on the Board of Supervisors. The 6-5 edge was secured with the swearing-in of new Supervisor Rafael Mandelman on Wednesday.

Breed, the city’s first female African-American mayor, will begin her work in Room 200 with both heightened urgency and the potential for a historic stretch of incumbency.

With another election set for November 2019, Breed will have precious little time to make progress on her priorities -- most notably, making a dent in the city’s homeless crisis.

But Lee’s sudden death late last year gives Breed the opportunity to finish his term and potentially run for two additional four-year terms of her own. If she holds office until 2028, Breed would become the city's longest-serving mayor since Angelo J. Rossi, who served from 1931 until 1944, before the implementation of term limits.

“She's being given effectively two practice runs with these two stints as acting mayor and then mayor,” said James Taylor, professor of political science at the University of San Francisco. “So she's being given plenty of opportunity to demonstrate her capacities as a governing executive.”

If she succeeds early, Taylor says, voters are likely to reward her with a decade of leadership.

“She has to hit the ground running,” he said.

Among the most pressing challenges is finding shelter and care for San Francisco’s homeless population.

Breed has promised to clear the city’s tent encampments within a year and build 5,000 units of housing annually across all income levels.

Accomplishing the latter could require a streamlining of the current housing approval process, which is easier said than done.

"The politics of 'no' has plagued our city for far too long," Breed said. "I plan to change the politics of 'no' to the politics of 'yes': Yes, we will build more housing."

Beyond policy aims, Breed has the opportunity to establish her independence from the tech and business interests that her opponents in the mayoral race claimed she lacked.

Taylor said Breed will face a challenge similar to Dianne Feinstein, who often sparred with anti-development advocates in the decade she served as mayor of the city.

Like Breed, Feinstein rose to leadership after tragedy, taking office after the assassination of George Moscone.

“There's always been a tension between pro-growth and slow-growth development in San Francisco,” Taylor said. “I think [Breed] will be powerfully informed by understanding how people reacted to Dianne Feinstein.”

On Wednesday, Feinstein left a video message for Breed, in which she recounted hearing a young Breed perform for her as part of the Benjamin Franklin Middle School band.

"Today, after far too long as the only woman mayor of San Francisco, I so proudly welcome you into the club," Feinstein said.