Given that Mr. Landrieu won more than half of the vote, a runoff election is not necessary.

In a city that is still mostly black, the victory was both startling in its departure from the past three decades of New Orleans history and predictable, in that Mr. Landrieu was the front-runner the moment he surprised the field and entered the race. He ran unsuccessfully for the post twice before, coming close in 2006 but losing the runoff to the current mayor, C. Ray Nagin, who is prevented by law from running for a third term.

Because his father oversaw the broad desegregation of the city, starting with a racially mixed brain trust that helped run City Hall, Mr. Landrieu has attracted strong support from black voters. Many residents also said they were drawn to his long political background, having grown weary with Mr. Nagin’s outsider approach, which has produced a painfully slow recovery from Hurricane Katrina in the years since 2005.

Of the more than 17,000 early ballots cast, a disproportionately high number of them were from black voters, said Greg Rigamer, an elections analyst, on WWL-TV, a local television channel. Mr. Landrieu won roughly two-thirds of these votes, Mr. Rigamer said.

It was a historic outcome of an erratic election, which did not generate much drama on a day-to-day basis but was punctuated every few weeks by sudden, shocking developments.

Initially, a series of prominent potential candidates, including Mr. Landrieu himself, said they were not interested in running. Then in December, at the last minute, Mr. Landrieu jumped in, throwing the race into chaos. Less than a month later, State Senator Ed Murray, one of the front-runners, surprised everyone by announcing his departure.