She was the first African American woman to serve in the United States Cabinet , and the first to enter the line of succession to the Presidency . She previously served as United States Ambassador to Luxembourg under President Lyndon B. Johnson , and was the first African-American woman to represent the United States as an ambassador .
She was the first African American woman to serve as a United States Ambassador , representing the U.S. in Luxembourg under President Lyndon B. Johnson , and the first to enter the line of succession to the Presidency .