Updated

Marking a first for Hispanics, the Democratic Party has chosen the mayor of San Antonio to deliver the keynote address at the Democratic National Convention.

The party announced Tuesday that Mayor Julian Castro would deliver the high-profile, prime-time address on the convention's opening night. First lady Michelle Obama will also address the convention delegates -- and a television audience across the country -- on the same night, Sept. 4.

Castro, 37, is the youngest mayor of a major U.S. city and the first Hispanic selected to deliver the keynote address at the Democratic convention.

President Obama is banking on Hispanic support in battleground states like Florida, Colorado and Nevada as he seeks to break away from Republican rival Mitt Romney. The race remains deadlocked just over three months from Election Day, though polls show Obama with a sizable lead over Romney among Hispanic voters.

The late-summer party conventions will set the tone for the fall campaign blitz. Obama will accept his party's nomination in Charlotte, N.C. the first week in September, while Romney will get the Republican nod in Tampa, Fla., a week earlier.

More On This...

As keynote speaker, Castro will step into the same role that propelled Obama into the national political spotlight. Then a little-known state lawmaker running for Senate from Illinois, Obama delivered the convention keynote in 2004, winning wide praise from Democrats as a rising star in the party.

Democrats have also announced that former President Bill Clinton and Elizabeth Warren, the party's Senate candidate in Massachusetts, will have high-profile speaking roles at the convention on Sept. 5.

Obama and Vice President Joe Biden will speak in prime time on the convention's final night during an event at an outdoor arena in Charlotte that is expected to draw a crowd of tens of thousands.