When she finally returned home, she was given a brand new telescope bought with money collected by women around the country for the first woman astronomer of the United States. She used it to study sunspots and other astronomical events.
In 1865 Maria accepted a position as professor of astronomy and director of the college observatory at the newly-opened Vassar College in Poughkeepsie, New York. She was delighted to learn that she would have the use of a twelve-inch telescope, the third largest in the United States. Continuing her own research, she studied the surface features of Jupiter and Saturn and photographed stars.
In 1869 she was the first woman elected to the American Philosophical Society. Four years later, she helped found the American Association for the Advancement of Women and served as its president from 1874 to 1876. The first meeting of the Women's Congress was held in 1873, with such notables as Elizabeth Cady Stanton, Susan B. Anthony, Lucy Stone, Dr. Elizabeth Blackwell, Antoinette Brown Blackwell, and Maria Mitchell in attendance. In 1875, Maria led the Women’s Congress. Throughout her life Maria encouraged young women just as her father had encouraged her, to be anything they wanted to be.
Poor health forced Maria to retire from Vassar in 1888. She died June 28, 1889 in Lynn, Massachusetts.
The Maria Mitchell Association was founded on Nantucket in 1902. In 1905 Maria was elected to the Hall of Fame of Great Americans at New York University (now at Bronx Community College). In 1994, she was inducted into the National Women's Hall of Fame in Seneca Falls, New York. Her birthplace on Nantucket is open to the public during the summer. Maria also has a lunar crater named for her.