Politicians and voter advocates nationally await his ruling, due this week, on whether to uphold Pennsylvania's new law requiring voters to show photo ID at the polls.
Republicans hope Simpson - elected as a Republican in 2001 - will validate the law, enacted by a GOP-controlled legislature and signed by a GOP governor. They see it as a reasonable means to prevent election fraud.
One GOP legislator, House Majority Leader Mike Turzai, said in June that a photo-ID requirement could help Mitt Romney defeat President Obama in Pennsylvania. Democrats have contended that is exactly what the law aims to do - hinder voting by poor people who might not have ID and who can't get it in time for the Nov. 6 election.
Simpson's decision in the case, then, is seen as politically pivotal.
"No matter what he does, there will be people who feel he was wrong," said Roy Shuman, former Republican chairman of Northampton County, where Simpson once sat on the Common Pleas Court bench.
If Simpson is feeling the heat, he isn't letting on.
Picking up the phone last week in his chambers, where he was working on his ruling, he said only that it was "not the time" for him to be talking to a reporter.
Both parties put great effort into winning appellate court elections in Pennsylvania - for Supreme Court, Superior Court, and Commonwealth Court. Some partisans appear to expect an ideological lean by their own judges in politically charged cases.
Many conservatives still burn over the key vote in June by U.S. Chief Justice John Roberts, a longtime Republican, that upheld Obama's health-care law.
Republicans also smolder over the January decision of Pennsylvania Chief Justice Ronald Castille, a Republican, to reject a new legislative district map that favored the GOP.
Shuman said he was content to have the issue in Simpson's hands.
"I've always known him to be a fair person. He makes his decision on the basis of where the law leads him, not on political ideology."
Shuman noted that, whichever way the decision goes, Simpson is immune from political reprisals. He just won another 10 years on the bench and would be too old - 70 - to legally run again.
A prominent Democrat said he, too, was content to have Simpson make the call.
T.J. Rooney, former state Democratic chairman, recalled that Simpson defeated his brother Joseph for a seat on the Northampton Court court in 1989. Simpson was a Democrat at the time. He switched after the election.
"My impression is he has always been a reasonable guy," Rooney said. "He is not a bomb-thrower. He is not a headline grabber. He has always been thought to be a rather solid person and a rather moderate person - and a pretty darn good judge."
Simpson, nicknamed Robin, was born in Harrisburg. He graduated from Freedom High School in Bethlehem in 1969. He went to Dickinson College and Dickinson law school, and then became a law clerk for Commonwealth Court Judge Glenn E. Mencer.
He practiced law for a few years, then was appointed by a Democratic governor, Robert P. Casey, to fill a temporary county court vacancy in 1989.
The same year, as only judicial candidates are permitted to do, he cross-filed to run for a full judicial term as both a Democrat and a Republican.
"Ironically," as Rooney put it, he was nominated by the Republicans in the spring primary, but not by his own party. He won again in November.
Peg Ferraro, former county GOP chairwoman, remembered that Simpson was kidded as "a man without a country" - not fully Republican or fully Democratic in the eyes of many.
He switched to the GOP as a matter of principle, she said.
"He looked at where each party was at the time and decided his positions were maybe a little bit more in tune with the Republicans."
After nearly a dozen years as a county judge, Simpson was elected to the state court. But he "never got a big head," Ferraro said.
Commonwealth Court, with 11 judges, handles most cases involving state government agencies, including election issues. It also hears appeals of local government issues and land-use cases.
The court sits in Philadelphia, Harrisburg, or Pittsburgh, but Simpson's personal office is in Nazareth.
Ferraro says she sees him working out, music in his ear, at the YMCA. Shuman remembers that at one time, "he ran every day with his dog until he ruined his feet doing it."
His wife is a recently retired school psychologist. The couple have two grown children.
As a judge - even as a judicial candidate - Simpson is not permitted to discuss politics.
Over the years, he has given expert legal analysis in lawyerly publications on land use, jury selection, and the free-speech rights of students.
Among his written court opinions so far this year are two that affirm the public's right to access to most state government records.
He was a member of a three-judge panel that upheld the right of the Allentown Morning Call newspaper to review a month's worth of e-mails among members of the Easton area school board.
He also granted a request by a citizen to review records the Game Commission had withheld from him.
Goutman, a trial lawyer, said Simpson is always a neutral umpire.
"He's extremely efficient, extremely hardworking, and extremely fair," Goutman said.
Another lawyer, Robert W. Gundlach Jr. of Warrington, said Simpson was "all business."
"I find Judge Simpson to be a very thorough and well-prepared judge," he said. "I find that he treats everybody respectfully and in a fair manner, and is not predisposed to make a decision before you appear before him."
Simpson, in recent hearings on voter ID, said his decision was not likely to be final, that one side or the other would appeal it to the state Supreme Court.
But Shira Goodman, deputy director of Pennsylvanians for Modern Courts, noted that the Supreme Court is evenly split along party lines, with three justices first elected as Republicans and three as Democrats.
"If the court splits, the lower court's decision stands," she said.
If that happens, Simpson would have the final word after all.
Contact Tom Infield at 610-313-8205, email@example.com, or follow on Twitter @tinfield.