State Sen. Bryan Simonaire was among the few Maryland lawmakers who donated to the effort opposing the measure. The Anne Arundel Republican was a leading opponent of the same-sex marriage measure when it was before the state legislature this year.
National advocacy groups contributed heavily on each side. The Human Rights Campaign donated $1.1 million to the effort to pass the measure. The National Organization for Marriage gave $1.2 million to the Maryland Marriage Alliance, which opposed Question 6.
Major contributions for opponents came from Roman Catholic groups, including $350,000 from the Knights of Columbus and dioceses in Arlington, Va., and Wheeling, W.Va.
William E. Lori, the Archbishop of Baltimore, gave $2,000 from his personal account. He gave "as a citizen of Maryland, a taxpayer and a believer in upholding marriage as between one man and one woman," said spokesman Sean Caine.
The donations by those who opposed the measure were not enough to get their message out, said the Rev. Derek McCoy, head of the Maryland Marriage Alliance. "A little bit more money, for sure we would have won," he said.
He said the national donor base was spread too thin because of gay marriage-related initiatives in three other states. He said his group's message was drowned out by ads for the other ballot questions in Maryland and that his side faced a formidable opponent in O'Malley.
"The governor was behind it," McCoy said, referring to the campaign in behalf of the law, a top O'Malley priority in Annapolis. "He did fundraising calls. He was calling people."
The total raised — about $8.3 million by the main groups on both sides of the marriage issue — paled in comparison with that spent by the opposing sides of the gambling expansion measure. That question attracted more than $93 million, mostly from two warring casino companies. The total is more than was spent on the past four Maryland gubernatorial races combined
MGM put up $41 million to support the gambling expansion proposal, while Penn National Gaming — which owns a West Virginia casino that stands to lose customers to Maryland — spent $44 million to oppose it.
Supporters of Maryland's Dream Act, a measure giving illegal immigrants access to lower in-state tuition, raised $1.7 million in their successful effort. The measure, Question 4, passed with nearly 60 percent of the vote and drew no formal opposition.
Contributors in support included Domino Foods, the Baltimore-based sugar company, which gave $100,000.
Stu FitzGibbon, the company's refinery manager, said: "In a nation of immigrants and a company that has grown in that tradition, we believe that an education is the one thing we give our children that cannot be taken away."
Baltimore Sun reporter Michael Dresser contributed to this article.
To search a database of donors on either side of the same-sex marriage debate, go to http://data.baltimoresun.com/marriage-donors/