Landrieu, a Democrat, became the first white to be elected to head the city since his father, Moon, who served as mayor from 1970 to 1978, The New York Times reported.
His victory shows the people of New Orleans wanted to "strike a blow for unity, strike a blow for a city that decided to be unified rather than divided, a city that understands where there is equal opportunity there is equal responsibility," Landrieu said.
Landrieu had 67 percent of the vote with more than half the precincts counted. His closest competitor, businessman Troy Henry, had only 13 percent.
Turnout was high in spite of competition from Mardi Gras and rallies for the Saints on the eve of the Super Bowl.
The incumbent mayor, Ray Nagin, won a second term in 2006 in spite of criticism of his handling of Hurricane Katrina, including his failure to plan before it hit and to help the city rebuild afterward. Nagin defeated Landrieu 52 percent to 48 percent in the runoff.
The Landrieus are one of Louisiana's leading political dynasties. Mary Landrieu, Mitch's sister, represents the state in the U.S. Senate.