Poll results released Tuesday by Gallup indicate 58 percent of American adults believe marijuana should be legal, compared to just 39 percent who believe the drug should continue to be illegal.
That's a 10 percentage point increase in support for legalization since Gallup asked the question in November 2012 and it's the first time more than 50 percent of respondents have told the polling firm they back legalization.
[CHARTS: ACLU Study Breaks Down Demographics of Pot Busts]
Ten years ago, in 2003, a mere 34 percent of adults told Gallup they supported legalization, and opponents held a 20 percentage point lead.
"The dramatically increasing support for making marijuana legal should come as no surprise. Marijuana prohibition has been an abject failure," said Rob Kampia, executive director of the Marijuana Policy Project, in a released statement.
[WATCH: McCain Says 'Maybe We Should Legalize' Marijuana]
"It is time for Congress to take this issue head on," he said. "It should no longer be considered scary or troublesome to speak out in support of more sensible marijuana policies. We need to put marijuana prohibition behind us, and our leaders need to step up to move things forward."
The poll surveyed 1,028 adults Oct. 3-5 and had a margin of error of plus or minus 4 percentage points. Data was not available for individual states.
Gallup Polling Data on Marijuana Legalization
| 1969 | 1985 | 1995 | 2003 | 2010 | 2012 | 2013 | |
| Percent supporting legalization | 12 | 23 | 25 | 34 | 46 | 48 | 58 |
| Percent opposing legalization | 84 | 73 | 73 | 64 | 50 | 50 | 39 |
Although legalization was most popular among young adults between the ages of 18 and 29 at 67 percent, a majority of respondents between the ages of 30 and 64 also backed legalization. Among those over the age of 65, 45 percent said they support legalization.
The results suggest an increase in public support for legalization since April, when the Pew Research Center found 52 percent support and 45 percent opposition to legalization.
[RELATED: Young Adults Left Behind by Colo., Wash. Marijuana Legalization]
Marijuana use is currently legal in two states for adults over the age of 21, and many other states have approved decriminalization or medical marijuana measures.
The Department of Justice announced in August it will not seek to block the opening of marijuana stores in Colorado and Washington state - scheduled to open early next year - so long as they are as tightly regulated as state officials anticipate.
[READ: D.C. Councilman Pushes Pot Legalization, Predicts Congress Would Allow It]
Numerous legalization bills were introduced by state lawmakers across the U.S. after the November 2012 referendum votes in Colorado and Washington, but so far none of have been successful.
A report issued in June by the American Civil Liberties Union said there were 784,021 arrests for simple possession of marijuana in 2010 - setting taxpayers back an estimated $3.613 billion in policing, court and jail costs.
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