Mitchell was born in Nantucket, Massachusetts, the daughter of William Mitchell, who started life as a cooper and became a school teacher and amateur astronomer of some distinction. Her brother, Henry Mitchell, became the leading American hydrographer. She herself was mainly educated by her father, whom she helped in the checking of chronometers for the local whaling fleet and in determining the longitude of Nantucket during the 1831 eclipse. From 1824 to 1842 she worked as librarian at the Nantucket Athenum and in 1849 she became the first woman to be employed full time by the US Nautical Almanac, with whom she computed the ephemerides of Venus. Finally, in 1865 she was appointed professor of astronomy and director of the observatory at the newly founded Vassar College.

Maria Mitchell was clearly fortunate to come from a highly talented family. She was also helped by coming from Nantucket, an area where women were expected to demonstrate an unusual degree of independence while the local men were absent on their long whaling voyages. It was also an area where it was common for the average person to possess a familiarity with mathematics, astronomy, and navigation.

She is mainly remembered today for her discovery, in 1847, of a new comet.