The Quinnipiac University poll found that 61 percent of voters support allowing same-sex couples to marry, compared to 33 percent opposed.
Support for marriage equality was 55-38 percent among men and 66-28 percent among women, 85-12 percent among Democrats and 63-30 percent among independent voters. Republicans are opposed 58-34 percent.
Support was highest among younger voters, 81-12 percent among those 18 to 29 years old. Among voters over 65, 44 percent support same-sex marriage and 48 percent are opposed.
The Quinnipiac poll was conducted April 15 to 21 and surveyed 1,298 registered Colorado voters. It has a margin of error of plus or minus 2.7 percentage points.