State Sen. Branden Petersen, R-Andover, said Thursday he will resign from the Senate next month, a move that will trigger a special election in his suburban district.

He had already decided over the summer that he would not seek re-election next year, and a handful of candidates have filed to run for his seat. They include former state Rep. Jim Abeler and GOP activists Andy Aplikowski and Donald Huizenga.

In an interview Thursday, Petersen said his decision to resign was motivated by the same reasons he decided not to run for re-election. Petersen said in July that the low pay for legislators and time commitment made it difficult to serve in the statehouse.

Legislators earn $31,140 annually, in addition to health benefits, a defined contribution pension plan, and a daily stipend for living expenses during legislative sessions.

“A few months ago I was deciding between whether I wanted to resign or simply not run for re-election,” Petersen said. “For many of the same reasons, I’m making the decision today.”

Petersen, 29, said finding a job that would give him several months a year to legislate was difficult. He said that as he enters his prime earning years, he’d like a secure job to provide for his family. He has a wife and three children under age 5. He now sells cars at an Elk River dealership.

He has criticized the part-time nature of his legislative job and its low pay, saying it has created a shallow pool of candidates and lawmakers who often are independently wealthy, lawyers or public employees whose collective-bargaining agreements guarantee them the ability to serve. The libertarian-leaning Republican was first elected to the House in 2010 and to the Senate in 2012. His support for same-sex marriage in 2013 angered Republicans in his district who said that they felt blindsided by his decision.

Petersen said his decision to step down would be best for his constituents, who are “better served when someone is there and not focused on the next thing.”

While in the Senate, Petersen earned a reputation for being a maverick on some issues, sometimes breaking with his caucus.

“Branden Petersen brought a unique and valuable perspective to the Republican Caucus and to the entire Senate,” Senate Minority Leader David Hann said in a statement. “His approach to the issues was always based on principle, not the prevailing political winds of the day. His leadership on privacy and criminal justice issues will be especially missed. We wish him well in his next endeavor and know he will be successful.”

Gov. Mark Dayton praised Petersen for his service, noting that “his exemplary demonstration of political courage was critical in securing marriage equality for all Minnesotans.”

Petersen was nine months behind on filing his 2014 campaign finance report and this week paid a $2,000 fine to the Minnesota Campaign Finance and Public Disclosure Board.

The first-term senator had amassed the maximum fine and civil penalty for the late filing, said Gary Goldsmith, executive director of the campaign finance board. Goldsmith said Petersen’s tardy file was unusually late, particularly for a sitting legislator.

Filed this week, the report shows two reimbursements to Petersen totaling $6,000 that Goldsmith said are too vague. “It’s not an issue at this point about whether it’s permitted,” he said. “It’s about the detail that has been provided.”

Petersen’s last day in the statehouse is Oct. 31.

Ricardo Lopez • 651-925-5044