On July 22, 1939, at the New York World's Fair, Mayor of New York City Fiorello La Guardia appointed 31-year-old Bolin as a judge of the Domestic Relations Court. For twenty years, she was the only black female judge in the country. She remained a judge of the court, renamed the Family Court in 1962, for 40 years, with her appointment being renewed three times, until she was required to retire aged 70. She worked to encourage racially integrated child services, ensuring that probation officers were assigned without regard to race or religion, and publicly funded childcare agencies accepted children without regard to ethnic background.