With 98.6 percent of the vote counted, the marriage amendment appears to have failed, MPR reported. The "nos" collected 52.4 percent of the vote, compared to 47.6 percent for the "yes" voters.

It was a historic first. Similar measures have passed in 30 states and have never been defeated, until now. Minnesotans United For All Families, the lead campaign against the amendment, tweeted this early Wednesday:

In fact, it appeared it was a huge night for gay rights advocates nationwide. Gay marriage was also on the ballot in Maryland, Maine and Washington. Reuters reports that Maryland voters on Tuesday approved same-sex marriage, the governor said, and a similar measure in Maine appeared on track to pass as well. Those votes would mark the first time marriage rights have been extended to same-sex couples by popular vote.

Exit polls indicate a strong majority of voters under 30 in Minnesota voted against the marriage ban, while other age groups were more closely divided, the Associated Press reports. A majority of women were against the ban while a majority of men supported it.

At issue in Minnesota was a ballot measure asking voters if the state should create a constitutional amendment defining marriage as between a man and woman. It would have prevented gay marriage from ever becoming legal in the state. (To be clear, unlike in Maryland and Maine, Minnesotans did not approve gay marriage – they defeated an amendment that would have banned it in the constitution.)

The two campaigns in the marriage amendment fight battled fiercely to the bitter end, spending the last week in one last all-out effort to motivate their coalitions and get them to the polls, the Star Tribune reported.

Opponents of the marriage amendment had their work cut out for them from the beginning. Through much of the campaign season, polls indicated the vote would be close, but that a majority of voters planned to vote in favor of the amendment. It was not until the final days that polls suggested a majority opposed it.

The marriage amendment was perhaps the most divisive and expensive ballot measure in the state's history, dividing people of faith, generations and sign-planting neighbors. Some wondered if the issue would pull voters to the polls and then swing other races.

Campaigns on both sides of the issue spent more than $16 million.