Levar Stoney will be the next mayor of Richmond.

Belying earlier polls that portrayed him as an also-ran in the contest, Mr. Stoney swept to a surprising outright victory in Tuesday’s election by capturing five of the nine City Council districts — the magic number.

He also won the largest slice of the citywide vote, 36 percent, against four opponents in claiming wins in the 2nd, 3rd, 5th, 6th and 7th districts on a night when many were predicting a deadlock resulting in a December runoff election to determine the city’s next chief executive.

Parlaying support from the Democratic establishment and younger voters, Mr. Stoney shocked the two pre-election favorites, according to the polls — attorney Joseph D. “Joe” Morrissey and former Downtown booster John F. “Jack” Berry.

A close associate of Gov. Terry McAuliffe and a former member of his cabinet, the mayor-elect is set to replace outgoing Mayor Dwight C. Jones on Jan. 1. He apparently will be the youngest Richmond mayor at age 35.

“It is my commitment, as the new mayor of the city, to inject fresh energy, a new approach and some new ideas to take this city to the next level,” Mr. Stoney said, claiming victory Wednesday night after the final votes were counted.

He promised to promote transparency and accountability and to focus on “improving the lives of Richmond children by strengthening our schools.”

“It is time for Richmond to have a mayor who tells our children they matter by investing in our schools, who tells our citizens they matter by connecting them with jobs and tells our families they matter by making sure we are providing them the premium services they deserve,” he stated in a Free Press interview ahead of the election. “People pay top dollar to live in Richmond; they need top dollar services.”

Starting out with 18 announced candidates, the race for Richmond mayor ended with eight names on the ballot and three with an opportunity to win. Three people dropped out of the race after the ballots were printed.

The race was among the most expensive in city history, with more than $1.7 million poured into the contest. Mr. Stoney and Mr. Berry raised the lion’s share, about $775,000 apiece.

Mr. Stoney appears to have won the election around 1:30 a.m. Wednesday when the Richmond Voter Registrar’s Office reported the results from the last few precincts.

However, he did not claim victory until around 8 p.m. Wednesday — nearly 20 hours later — after the registrar’s office posted results from the delayed count of 7,438 absentee ballots.

Mr. Morrissey, who won the 8th and 9th districts and trailed in the popular vote with about 20 percent, conceded the race around 10:30 p.m. Tuesday when it became clear he could not win five districts and had won too few votes to be in a runoff.

Mr. Berry, who won the 1st and 4th districts and was second in the popular vote, with about 34 percent, conceded after the absentee votes came in and showed he would not overtake Mr. Stoney in the 3rd District, which Mr. Stoney won by 600 votes.

The tallies on the city government website indicate Mr. Stoney defeated Mr. Berry in the popular vote, 35,525, or 36 percent, to 33,447 votes or 34 percent. Mr. Morrissey was a distant third with 20,995, or 21 percent.

Mr. Stoney apparently benefited from two events in the final days before Richmonders went to the polls.

First, Mr. Morrissey became engulfed in another sex scandal involving a former client who claimed he had propositioned her. Despite his denials, the high-profile scandal appeared to have cost him dearly at the polls after months of being considered the front runner.

Then, just a few days before the vote, another candidate, City Councilman Jonathan T. Baliles, dropped out and endorsed Mr. Stoney.

Mr. Stoney fueled his candidacy with his personal story of rising from tough early circumstances to high achievement. Born in New York, he grew up in York County under the care of his grandmother and his late father.

In his online biography, Mr. Stoney, who played quarterback on his high school football team, noted he was the first in his family to earn a high school diploma and a college degree.

A graduate of James Madison University, where he was the first African-American to lead the student government, Mr. Stoney began his climb in 2004 when he worked as an organizer for Democrat John Kerry’s presidential campaign and then became a Governor’s Fellow in then-Gov. Mark Warner’s administration.

He went on to work for the Democratic Party of Virginia in 2006, first as political director and then as executive director, where he won attention for his efforts to elect Barack Obama president in 2008.

In 2013, he became deputy campaign manager for Gov. McAuliffe and then deputy director of the McAuliffe transition team.

His reward from Gov. McAuliffe was his appointment as state secretary of the commonwealth, the first African-American to hold the post. For two years, he managed the governor’s appointments to boards and commissions and also led the administration’s efforts to expand the restoration of the political rights of released felons.

Last April, Mr. Stoney quit to begin his campaign for mayor, with the support of Gov. McAuliffe, who rallied donors and Democratic support for his protégé.

Mr. Stoney said that his ability to win was fueled in part by his taking the 2nd District, which had been expected to back Mr. Berry.

He praised the students of Virginia Commonwealth University “who came out in force and supported my candidacy,” enabling him to win that district.

The ambitious Mr. Stoney is considered a rising Democratic star who is likely to be considered for other offices in the future. He hopes he can leave his mark on Richmond.

Unlike Mr. Berry, a former deputy city manager in Richmond and a former county manager in Hanover County, Mr. Stoney will start out with little experience in city operations.

He is ready to begin his education, though, which could lead to changes in the administrative team that Mayor Jones has assembled.

“I will be starting to build my transition team in the upcoming days,” he said Wednesday evening, “and then we’ll start looking at personnel and looking at a comprehensive performance audit review to ensure we can find the right personnel and strengthen some of the programs in City Hall.”