The system set up for the April 22 election for mayor and other city positions makes it difficult for displaced voters to cast a ballot, Jackson and other activists said.
"We want the Voting Rights Act," Jackson said at a news conference before the rally. Black leaders have argued city elections could violate the landmark 1965 law.
The city election could have a broad effect nationwide, Sharpton said: "What happens in New Orleans will affect voting rights all over the United States."
Jackson and other activists are demanding satellite polling places for displaced voters in cities outside New Orleans, and even outside Louisiana. Fewer than half of the city's 460,000 residents have returned since the Aug. 29 storm flooded the city.
Activists also urged the release of updated lists of displaced voter addresses, a request the Federal Emergency Management Agency has denied, saying it would breach privacy.
About 2,000 people attended the rally and march, said New Orleans police Capt. Juan Quinton.
The rally was held at the convention center, site of some of the most vivid scenes of desperation out of Hurricane Katrina. It included state and federal lawmakers and comedian Bill Cosby, who urged residents to rebuild without the murders and drug dealing that plagued New Orleans before the storm.
"It's painful that we can't heal ourselves unless we cleanse the wounds," Cosby said.
After the rally, protesters marched across a Mississippi River bridge where residents trying to leave the city after Katrina were turned back.
A lawsuit filed by two state legislators claims police in the city of Gretna used excessive force when refusing to let fleeing evacuees cross. State prosecutors are also investigating allegations of civil rights violations.
Gretna officials continue to defend the decision, saying they lacked the resources to feed or shelter evacuees and could not ensure their safety because of hurricane damage.
"The symbolism of crossing the bridge is dead wrong, mainly because of the conditions after the storm," Gretna Mayor Ronnie Harris said. "They're marching to an area to that had nothing to offer."
Lurking beneath the surface of Saturday's rally was a discussion of poverty.
When Katrina struck Aug. 29, thousands of people who had not known loss suddenly knew what it was like to be homeless and jobless. To taste hunger and feel thirst. To go without medical care or even toilets.
And those who didn't experience the misery and chaos firsthand saw it in graphic detail every day and night on television. The desperate, angry masses at the Superdome and convention center. The rampant looting. The floating bodies.