After she became famous, she wrote articles in the St. Louis Post-Dispatch about the conditions of the poor. She became a member of the American Civil Liberties Union, the Urban League and, with Fannie Cook, worked on the St. Louis Committee for the Rehabilitation of Sharecroppers. She also volunteered, painting murals at the Mission Free School and the Turner School for the Disabled and Delinquent Negro Children.

Johnson was married twice. Her first husband was an attorney for the National Labor Relations Board and they divorced in 1941. Her second husband initially worked for the NLRB and, after WWII, became editor of the Farm Quarterly. In 1970 Johnson was awarded an honorary doctorate of humane letters from Washington University.