With nearly three-quarters of Nevada's population, Clark County plays a significant role in determining statewide Nevada elections as well the winner of the state's electoral votes in presidential elections. At the presidential level, the county, like most urban counties nationwide, leans Democratic. The last Republican to carry the county was George H.W. Bush in 1988. However, it is somewhat less Democratic than many other urban counties; the GOP candidate has received at least 39 percent of the vote at every election since 2000. This Democratic trend predates the county's explosive growth in the second half of the 20th century. Republican presidential candidates have only won the county six times from 1912 to the present day, all coming in national landslides where the Republican won over 400 electoral votes.

At the statewide level, however, the county is more of a swing county, with several Republican gubernatorial candidates and U.S. Senators winning the county since the late 1980s. The last Republican senator to win the county was John Ensign in his 2006 victory, even as Jim Gibbons lost it in his gubernatorial win over Dina Titus that year. Both Kenny Guinn and Brian Sandoval carried the county in both gubernatorial terms they won, however.

In 2018, Dean Heller carried 15 of Nevada's 17 county-level jurisdictions in his bid for a second full term in the U. S. Senate. Democratic challenger Jacky Rosen won Clark county. In that year's gubernatorial election, Democrat Steve Sisolak lost 15 out of 17 county-level jurisdictions, but won Clark. Since 2008, the Democratic presidential candidate has won Clark by more than enough votes to carry Nevada.

The city of Las Vegas itself leans Democratic, as do the communities of Paradise, Spring Valley and Enterprise. The city of North Las Vegas and the communities of Sunrise Manor, Winchester and Whitney are more strongly Democratic, while the city of Henderson and the Summerlin South community have a Republican lean. Boulder City, where gambling is prohibited, leans Republican. Outside Las Vegas Valley, the county leans Republican.