A year after stepping down as chief justice of the Supreme Judicial Court, Margaret H. Marshall is returning to private practice in Boston as senior counsel at Choate Hall & Stewart.
Marshall, who wrote the landmark 2003 decision that made Massachusetts the first state to legalize gay marriage, will work part time beginning this week. The schedule allows her to continue to spend time with her husband, former New York Times columnist Anthony Lewis, who has Parkinson’s disease.
Marshall, 67, who served as chief justice from 1999 to 2010, will focus on the firm’s community outreach, pro bono, and diversity efforts, as well as provide counsel on special projects.
“We have had a wonderful year together,’’ Marshall said of her husband, “but I have always wanted to be able to give back in some way for the enormous opportunities that this country, and this Commonwealth, and this town have given to me. But I had to do it in a way that would allow me to keep that flexibility.’’
Marshall, who lives in Cambridge and is a native of South Africa, will also teach at Harvard Law School as a senior research fellow and lecturer.
By working at Choate Hall, Marshall will return to a firm where she was a partner before being named vice president and general counsel at Harvard in 1992.
Marshall cited the “deep friendships’’ she had made at Choate Hall and its important role in her career as factors that contributed to her decision to work in private practice.
“What I wanted to do was to leave the court with no commitments going forward, to really spend the time with Tony, and for the two of us to figure out what was and wasn’t possible,’’ Marshall said.
What became clear, she said, was her desire to remain engaged with the law provided she could fashion a flexible schedule.
Governor William F. Weld appointed Marshall to the SJC in 1996. Three years later, Governor Paul Cellucci named her the first woman to serve as Massachusetts chief justice.
Marshall wrote more than 300 opinions for the high court, including the historic case of Goodridge v. Department of Public Health, which legalized gay marriage in Massachusetts.
The 4-3 majority of SJC justices based its decision on the equal protection and due process provisions of the state Constitution.
“The Massachusetts Constitution affirms the dignity and equality of all individuals,’’ Marshall wrote. “It forbids the creation of second-class citizens.’’
Other rulings included a 2006 decision that said cigarette makers cannot defend against personal-injury lawsuits by arguing that smokers should know the health risks of cigarettes.
Marshall earned a bachelor’s degree in 1966 from the University of the Witwatersrand in Johannesburg, where she was a student leader in South Africa’s antiapartheid movement.
She received a master’s degree in education from Harvard University in 1969 and a law degree from Yale in 1976.