In a statement Wednesday, Hagan said she has a great deal of respect for varying opinions on the issue.
"After much thought and prayer, I have come to my own personal conclusion that we shouldn't tell people who they can love or who they can marry," she said.
Hagan, a Greensboro attorney, former banker and ex-state senator, said her decision didn't come overnight.
"Last year, I opposed Amendment One because I was concerned about the negative consequences it could have on North Carolina families and our economy," she said. "The fabric of North Carolina and what makes our state so special is our families and our common desire for a brighter future for our children. No matter what your family looks like, we all want the same thing for our families -- happiness, health, prosperity, a bright future for our children and grandchildren."
North Carolina Amendment 1 proposed to amend the state constitution to limit the types of domestic unions valid or recognized. North Carolina voters approved the amendment last May. State law already defined marriage as being between a man and a woman.
"Religious institutions should have religious freedom on this issue," Hagan added. "No church or minister should ever have to conduct a marriage that is inconsistent with their religious beliefs. But I think as a civil institution, this issue's time has come and we need to move forward."
The senator said jobs and the economy are her number one issues right now.
"I'm not going to take my eye off that ball at a time when so many are still struggling," she said.
Hagan is up for re-election in 2014.