Support for gay marriage has never been higher as the U.S. Supreme Court is set to rule whether it is constitutional for states to ban same-sex marriage laws, a new NBC News/Wall Street Journal poll found. About 6 in 10 Americans favor gay marriage, the poll found  -- an all-time high and almost twice the support of the 30 percent of Americans who said they felt that way in 2004.

Democrats and young people are the strongest supporters of gay marriage. Nearly three-fourths of both groups favor same-sex marriage, the poll found. While a minority of Republicans -- 40 percent -- support same-sex marriage, their support for gay marriage has been sharply trending upward. Only 27 percent of Republicans favored same-sex marriage in 2013, according to the Wall Street Journal.

Other groups whose support for gay marriage is on the uptick are Hispanics and people without college degrees, according to the poll. Conservative support for same-sex marriage has increased by 9 percent since 2013, from 26 percent back then to 35 percent today.

Nearly 80 percent of respondents said they either personally know or work with someone who is gay or lesbian -- a 15 percent increase from the 62 percent who said so in 2004.

The poll of 1,000 adults, which was conducted March 1-5 and has a margin of error of plus-or-minus 3.1 percentage points, was released as the Supreme Court is set to decide on same-sex marriage later this year.   

Up for debate is whether states with bans on same-sex marriage are in violation of the constitution. A 2013 landmark case, United States v. Windsor, struck down the Defense of Marriage Act and forced the federal government to recognize same-sex marriages. The court will now hear whether state bans on same-sex marriage defy the constitution. Debate is set to begin in April.