Though ostensibly non-partisan, the 6,000-member crowd was overwhelmingly and vocally behind John Kerry's bid for the White House.
"This year we're not going to sit on the sidelines and complain, we're going to decide the next president of the United States," Combs told the crowd gathered on Gullen Mall.
Said DiCaprio: "We are at a turning point. This is not just an election to decide a single president. ... The power of our vote will determine the direction of the most powerful court in the world."
When he told the crowd, he supports John Kerry, many began chanting "Kerry, Kerry."
2014: The Year in Music [PHOTOS]