Kemp is carefully reviewing the decision, a spokesman said.
Johnson's candidacy was challenged by Matt Metcalf of Roswell, who filed a complaint with the Secretary of State's Office. He said Johnson was ineligible to hold office because he owed more than $15,000 in state and federal taxes.
According to the Georgia Department of Revenue, Johnson owes $3,638 in taxes. The IRS says he owes $11,447 in taxes.
Johnson has acknowledged being delinquent on his taxes, but he has been making payments on his past-due federal taxes to the IRS and he will make his first payment to the state on July 28, Davis said.
The problem, however, is that Johnson failed to remedy the problems before he formally filed his notice of candidacy, Judge Malihi said in his decision. "Accordingly, he did not meet the qualification for office at the time he swore that he was eligible to hold office."
Johnson is a former attorney for Fulton County and the city of Atlanta. Last year, Gov. Nathan Deal appointed Markle to fill the unexpired term of Michael Johnson, who resigned to run for Congress; at the time, Markle was Deal's executive counsel.
Staff writer Chris Joyner contributed to this article.