"North Dakotans — with a strong and clear NO vote — affirmed that religious liberty is securely protected in the U.S. Constitution," Sarah Stoesz said in a statement.
"Measure Three was divisive, unnecessary and could have had dangerous consequences," she said.
The effort was supported by conservative Catholics but predated controversy over the Obama administration's birth-control coverage mandate, according to reports. It was widely opposed by women's groups, anti-abuse groups and the body that governs many Lutheran churches in the state.
Measure 3 "will seriously undercut protection for children in our state by opening the door for people to claim religious freedom as a justification for maltreatment," he said.
Other opponents argued that single women who become pregnant, or women who want their birth control covered by their insurance, could face discrimination from employers as a result of the law.
A supporter of the measure — Christopher Dodson, who heads the North Dakota Catholic Conference — said in response that the law would not affect "acts which the state has a compelling interest in preventing."
"It's somewhat irresponsible to even imply that the state doesn't have an interest in protecting children, women and vulnerable persons," Dodson added to NPR.
Dodson later blasted Planned Parenthood for pouring a "massive amount of out-of-state money" into the campaign against Measure 3.
The move "confirms that religious freedom in North Dakota is not safe," he said in a statement to The Forum of Fargo-Moorhead following Tuesday's vote.
In its own statement, NARAL Pro-Choice America noted that the defeat marks the "10th pro-choice victory out of the 11 ballot measures affecting reproductive rights [nationwide] … since 2005."