The mayor told the City Council on Wednesday afternoon that he was leaving. He later released a news release on his decision. (Read the entire statement here.)
"I feel we have faced up to tough challenges and we have accomplished great things for our city," said Leppert. "Now I feel I can better serve Dallas, our region and the state of Texas in a new capacity."
Leppert, a Republican, said he will have more to say about what other role he means in the coming days.
There has been speculation that he will run for the U.S. Senate seat being vacated by Sen. Kay Bailey Hutchison, who said last month that she will not run for re-election.
In his place, Mayor Pro Tem Dwaine Caraway will become the acting mayor until a new mayor is sworn in on June 27.
Caraway's title is an honorary post granted by fellow council members that puts him first in line to become interim mayor until a new mayor is elected. With rumors circulating that Leppert may step down, opponents of Caraway lobbied last week to stop him from becoming interim mayor after he gave Philadelphia Eagles quarterback Michael Vick, a convicted felon, a key to the city of Dallas.
Leppert cited a 25 percent drop in crime, economic development in the city, improved education and the Mayor's Youth Fitness Initiative among his accomplishments during his tenure.
"History will look back on this time and reveal the tremendous achievements, advances and strides that we've made -- and see these have been some of the most productive years in city history," said Leppert.
Leppert is ending his term as mayor four months before the end of his first term. He had previously announced that he would not seek a second mayoral term.
Election Day is May 14. If need be, a runoff will be June 18.
Editor's Note: We initially reported that Leppert's resignation was to be effective Wednesday. We regret the error.
NBCDFW's Ken Kalthoff contributed to this report.