Landrieu said the four monuments were out of step with a modern city that embraces people of all races while acknowledging that New Orleans was also once one of the biggest slave markets in America.
Landrieu called for the monuments' removal in the lingering emotional aftermath of the 2015 massacre of nine black parishioners at a SC church.
City officials haven't announced immediate plans to rename either Lee Circle or Jefferson Davis Parkway, where the Davis statue was located.
"It's not good to continue to revere a false version of history and put the Confederacy on a pedestal", Landrieu, who is white, said in an interview with The Associated Press.
Since May 11, crews have removed monuments to Jefferson Davis, president of the pro-slavery Confederacy and P.G.T. Beauregard, a Confederate general.
Those three statues were taken down in the pre-dawn hours without advance public notice, a precautionary measure after officials said threats were made against contractors and workers involved.
In a speech about the removal of the monuments, the mayor said they were landmarks that were not a true reflection of the city.
Michael "Quess" Moore co-founded the group Take "Em Down NOLA, which led New Orleans" charge to remove its Confederate statues.
"I knew that taking these monuments down was going to be tough", Landrieu said.
Workers tied ropes around a towering statue of Gen. Robert E Lee, preparing to take down the last of New Orleans' four Confederate monuments Friday as hundreds looked and some danced in the streets.
The city will begin a competitive RFP process to decide where the statues will eventually go. More than 100 supporters of the removals were on hand listening to a jazz band, not unlike behavior at city parks in New Orleans on any Friday.
The Robert E. Lee statue was a familiar landmark for tourists and commuters who travel busy St. Charles Avenue by auto or on one of the city's historic streetcars.
A Southern Poverty Law Center study previous year identified more than 1,500 Confederate symbols on public property, including "monuments and statues; flags; holidays and other observances; and the names of schools, highways, parks, bridges, counties, cities, lakes, dams, roads, military bases, and other public works". The statue, which stood for 106 years, had been atop a roughly 12-foot column and depicted Davis with his right arm outstretched with palm turned upward.
Seriously, Mitch? So, people are literally fleeing the city because of Confederate monuments?
The process was delayed for almost two years by a succession of lawsuits from historic preservation groups and monument supporters.
Of the Confederate past, he said: "It's my history, but it's not my heritage". The local chapter of the Sons of Confederate Veterans sued the city in an effort to block the plan, and in March a U.S. Court of Appeals found in favor of the city, clearing the path for removal.
They are all gone now.
The city appeared to be building a temporary structure to cover and protect the monuments at that location until a final resting place is decided upon.
The selection process would require public bids, only nonprofits and governmental entities can bid on the statues, they must be displayed in historical context and the statues cannot be displayed outdoors on public property in Orleans Parish.
The city plans to leave the column where Lee's statue stood intact and will mount public art in its place.
Earlier, with work underway, Mayor Mitch Landrieu explained the city's reasons for removing the statue and other monuments at a private address. But he insisted the statues must go.
The city wants to finish the work during its tricentennial year in 2018.