Donald F. McGahn, the controversial former chairman of the Federal Election Commission, resigned from the panel on Tuesday to return to private law practice, ending what campaign-finance reform advocates and political practitioners called one of the most consequential tenures in the commission’s 38-year history.

McGahn, a Republican who had served on the FEC since 2008, clashed frequently with Democrats as he helped push a conservative interpretation of campaign-finance laws and persistent skepticism about government oversight of political campaigns.

McGahn will leave to become a partner at Patton Boggs, which has one of Washington’s leading election law practices.

In an interview, McGahn cited his work on FEC procedures as his most enduring legacy. McGahn pushed to allow campaigns and party committees to present their sides of cases in open session rather than behind closed doors.

“The procedures are completely different. It’s much more of a fair place, an honest place,” McGahn said. “There’s much more of an opportunity to do legal briefing and real arguing.”

McGahn’s term had expired in 2009, but he was not replaced until this year amid a state of general gridlock at the agency.

The Senate Rules Committee on Tuesday unanimously approved his intended replacement, attorney Lee E. Goodman, along with Ann Ravel for an open Democratic seat. Both nominees are expected to easily clear the full Senate.

McGahn served on the FEC at a time of rapid change in campaign-finance law. The past several years have given rise to an explosion of outside spending, from 501(c)(4) organizations to super PACs. The Supreme Court also struck down several provisions of the 2002 Bipartisan Campaign Reform Act, better known as McCain-Feingold, forcing the FEC to rewrite some of its rules.

McGahn led a bloc of three Republicans who almost always voted together. Campaign-finance reform advocates and editorial boards were often critical of what they characterized as McGahn’s efforts to chip away at election rules and regulations.

McGahn also pushed unsuccessfully this year for rules that would have barred FEC lawyers from sharing information with federal prosecutors without commission approval. The FEC’s top lawyer abruptly resigned amid feuding over the proposal.

But many lawyers who argued before the commission also say they viewed McGahn as an ally because of his expertise and because he pushed for more open deliberations.

“Don has been one of the most consequential commissioners the FEC’s ever had,” said Marc Elias, a Democratic attorney at Perkins Coie. “He has his supporters and he has had his detractors, but that’s largely because of how successful he has been as a commissioner in reframing important parts of the agency. . . . He often brought a perspective of the practical impact of the law on candidates and parties that was important.”

McGahn had been the general counsel at the National Republican Congressional Committee for nearly a decade before being appointed to the FEC, and he briefed Republican members of Congress on campaign-finance legislation when McCain-Feingold passed the House in 2002.

To campaign-finance reformers, McGahn’s position enabled him to push for more deregulation. McGahn voted several times to relax restrictions on political money the parties can use for recounts and litigation, and he won over some Democratic commissioners by framing the funds as money that could be spent on voting rights cases.

The GOP bloc of Republican votes almost always held firm — largely, McGahn said, because he and his two colleagues were of similar ages and backgrounds.

The three Democratic commissioners who served alongside McGahn for most of his tenure came from different backgrounds: Ellen L. Weintraub, the current FEC chairwoman and a frequent McGahn foe, served as a counsel to the House Ethics Committee. Steven T. Walther was a Reno lawyer and a longtime ally of Senate Majority Leader Harry M. Reid (D-Nev.). And Cynthia L. Bauerly, who left the commission earlier this year, served on the Senate Judiciary Committee under Sen. Charles E. Schumer (D-N.Y.).

What McGahn sees as transparency, campaign-finance reformers see as more deregulation.

Paul S. Ryan, an attorney for the Campaign Legal Center, a watchdog group, says the FEC’s new policy of accepting requests for advisory opinions on gray areas in existing law opens the door to special-interest groups pushing for new ways to spend money.

“Some of the processes have been opened up, but not in a way that I would consider to be fair and open,” Ryan said. “Mr. McGahn and his colleagues on the commission have, to some extent, slanted the field in favor of those who seek deregulation.”

McGahn said there’s a clear culprit in the explosion of outside money in politics: the ­McCain-Feingold law itself. Because the law eliminated unlimited “soft money” contributions, party spending has become so limited that outside groups are picking up the slack.

“The parties became less important because their spending is limited,” McGahn said. ­“McCain-Feingold has taken the parties out of it to a large degree.”

He added, “How come everybody doesn’t have the same size megaphone? It’s the parties with the smaller megaphone.”