Johnson emphasized civil rights and legal assistance to the poor. After passing the bar, she became the managing attorney at the New Orleans Legal Assistance Corporation, serving from 1969 to 1973. In 1984, she was elected to the Orleans Parish Civil District Court, the first woman to serve as a judge in that court. She was re-elected in 1990 and in 1994 attained seniority, gaining the position of chief judge of that court. Johnson ran unsuccessfully for the Fourth Circuit Court of Appeal in the nonpartisan blanket primary held on October 1, 1994. In Chisom v. Edwards, a suit started in 1987 and brought under the Voting Rights Act of 1965, the federal court found that the state's "system for electing justices diluted black voting strength" in the way that the districts were defined, in violation of the VRA. In 1987 the First Supreme Court District included Orleans and three other parishes. Two justices were elected at-large from this district, which had a white majority population around New Orleans. But Orleans Parish population comprised the majority of the district and was majority African American. The plaintiffs contended that this system diluted their vote, preventing them from electing candidates of their choice. They sought a remedy to have the district divided into two: one for Orleans Parish and one for the other three parishes. In Clark v. Edwards, a suit was brought against the state by black lawyers, who argued that the system of judicial election discriminated against them. The court heard expert testimony as to racially polarized voting in Louisiana, for judicial seats as well as other positions, and how few African Americans were elected to judicial positions under the at-large system. Whites did not vote for black candidates, even by a plurality. The court noted that "black citizens comprise about thirty percent of Louisiana's population lack lawyers now hold only 5 of the 178 district court judgeships and only 1 of 48 court of appeal judgeships." Analyzing districts to determine where there were problems in minority vote dilution, the court formulated a federal consent decree that established sub-districts within some judicial districts. The consent decree operated from 1992 to 2000, establishing a sub-district in Orleans Parish, with the other sub-district covering the three parishes outside, and therefore adding an eighth position to the Supreme Court, known as the "Chison seat". Johnson was appointed in 1994 as the eighth associate justice to the State Supreme Court under this settlement. In 2000 the state was allowed to revert to seven judicial districts in its election of the State Supreme Court; Johnson ran for the reconfigured 7th Supreme Court District that year, and was elected in her own right. She was re-elected to this seat in 2010. The Louisiana Constitution of 1974 directs that the longest-serving associate justice becomes chief justice should a vacancy occur prior to the next regular election. In 2012 the position of chief justice was going to open based on the incumbent's retirement. Associate Justice Johnson was eligible by strict seniority to become chief justice, but Judge Jeffrey P. Victory, a Republican from Shreveport, also sought the position. Johnson claimed the right to succeed Kimball under the state constitution. Justice Victory had maintained that he was the legitimate successor because he was elected to the Supreme Court on November 8, 1994, and had previously been a judge of the Second Circuit Court of Appeal for four years. Johnson's tenure on the Supreme Court preceded that of Victory by less than three months. When her colleagues on the court said that they were going to debate the eligibility of the two candidates, Johnson filed a federal suit on the issue in July 2012. United States District JudgeSusie Morgan ruled in September 2012 that Johnson had the greater seniority under the state constitution. In October 2012, the state Supreme Court members declared that Johnson would succeed Kimball because the start of Johnson's tenure predated that of Victory. They concluded that her seniority was more important than the fact that she had not gained her seat on the Supreme Court by election. Johnson is the first African American to serve as chief justice in Louisiana. She is the first African-American woman to serve on the Louisiana Supreme Court as both associate justice and chief justice. Justice Victory retired from the Supreme Court on December 31, 2014. He was succeeded by Republican, Scott Crichton, a former Louisiana 1st District Court judge from Shreveport.
