Unofficial returns showed Nahmias winning 68 percent of the vote compared to 32 percent for Lawrenceville attorney Tammy Lynn Adkins with 92 percent of precincts reporting in the nonpartisan race.
Nahmias, 46, beat Adkins, 47, in the Nov. 2 general election but were forced into a runoff since neither candidate received 50 percent plus one vote as required by law.
Republican Gov. Sonny Perdue appointed Nahmias to the bench in August 2009 to replace retiring Chief Justice Leah Ward Sears, the first woman appointed to the court.
During the campaign, he touted his Republican credentials as a former clerk for U.S. Supreme Court Justice Antonin Scalia. He also served as a leading terrorism prosecutor in the U.S. Justice Department until President George W. Bush appointed him U.S. attorney in Atlanta in 2004.
Adkins finished third in a 2008 Court of Appeals race. She mostly skipped campaign events, rarely granted interviews and did not bother creating a website ahead of November's general election. She said she could not afford to take time off from her law practice to campaign and instead relied on name recognition from her previous runs.
She specializes in custody cases and has never argued before the Georgia Supreme Court.
Scott Sanders, 62, an attorney who practices entertainment law, was one of two voters who cast ballots at an Atlanta polling station over the course of an hour. He wouldn't say whom he supported in the top race, but was surprised that Adkins made it to a runoff without seriously campaigning.
"We really were laughing about it in our office, that we ought to get on the ballot next time because if you can come in second, not have put up a sign, not raise a dollar, never give a speech, I mean, why not?" Sanders said.
Besides selecting a new state Supreme Court justice, voters selected McFadden for an open seat on the state Appeals Court. He garnered 63 percent of the vote compared to 37 percent for Antoinette Davis, a 59-year-old attorney from Marietta, with 92 percent of precincts reporting.
Also Tuesday, voters decided three state Superior Court seats in Atlanta, Macon and Stone Mountain and selected two district attorneys for the Houston and Macon circuits.