Last year’s Senate race between Elizabeth Warren and Scott Brown was the most expensive in U.S. history. According to the Center for Responsive Politics, the two candidates raised a jaw-dropping $76 million, combined, and spent an even more jaw-dropping $82 million.

Those figures make it hard to think of that race as a model for healthy campaign finance reform. But a new report by the good-government group Common Cause Massachusetts makes the case that one key element of the campaign, the so-called “People’s Pledge” taken by Brown and Warren, yielded significant positive results. According to the report, A Plea for a Pledge, the agreement “increased disclosure of donors, decreased wealthy donor influence on the electoral process, and reduced the amount of negative advertising.”

Indeed, Common Cause argues, it was so effective that it should be adopted in other races—starting with the contest between U.S. Rep. Ed Markey and Gabriel Gomez for the Massachusetts Senate seat vacated earlier this year by John Kerry.

The Warren/Brown pledge came at a time when evidence of the deleterious effects of the Supreme Court’s 2010 Citizens United decision was fast accumulating. That ruling, which lifted government restrictions on certain political expenditures by corporations, labor unions and other organizations, led to unprecedented political spending by outside groups—$1.3 billion in the 2012 federal election cycle alone.

In their pledge, Warren and Brown attempted to diminish the role of third-party groups by agreeing that if an outside group advertised on behalf of either of them, that candidate would pay a financial penalty, with the money given to a charity of the other candidate’s choice.

“We’re living in a world right now where the Supreme Court has essentially told us that we’re not allowed to legislate campaign finance, we’re not allowed to limit the amount of undisclosed contributions,” Tyler Creighton, assistant director of Common Cause Mass. and author of A Plea for a Pledge, told the Advocate. “The People’s Pledge was really a testament to the fact that there are things we can do that, while not perfect, help to make our elections more transparent.”

The report highlights the positive effects of the Brown/Warren agreement by comparing their race to pledge-less Senate races in other states. For instance, outside spending accounted for just 9 percent of total spending in Massachusetts while accounting for 47 percent of spending in Ohio’s Senate race, 62 percent in Virginia and 64 percent in Wisconsin.

In Massachusetts, $3.3 million of the money spent was from undisclosed donors—“dark” money—a figure dwarfed by the dark money totals in Wisconsin ($13.6 million), Ohio ($14.1 million) and Virginia ($19.8 million). And small donations ($200 or less) far outmatched donations from outside groups in Massachusetts—$23.5 million total, versus $8 million. In the other three states examined, outside groups outspent small donors by a margin of five to one.

The People’s Pledge was especially effective at blocking spending by the sorts of secretive, well-funded political groups that have multiplied like rabbits since the Citizens United decision, Creighton said. “All we know is this group sprung up out of nowhere that has this name—‘Americans for Cupcakes and a Better World.’ You have no idea who that is,” and no way of tracking what interests are behind that money, he said.

As Markey and Gomez head toward their June 25 special election. Common Cause is calling on them to adopt their own People’s Pledge. Markey, the Democratic candidate, has said he would do so. Gomez, a Republican, has refused, saying in a press release, “I’m taking one pledge and one pledge only: to protect and defend the Constitution.”

Gomez also slammed Markey for accepting millions in special interest money over his long tenure in Congress. While Markey has supported multiple campaign-finance reform bills in his career, he’s also accepted donations from political action committees and lobbyists for the telecommunications and finance industries, among others.

The successes of the People’s Pledge notwithstanding, “Big money is still winning the day at the very end,” Creighton said. “The People’s Pledge is a short-term fix. It’s not the ultimate goal.”

That ultimate goal, for Common Cause and like-minded groups: a Constitutional amendment that would overturn the Citizens United decision and a public financing system that would take corporate and other special interest money out of the political system.•