After graduating from both Amherst College and Harvard Law School, he joined his father, Edward Dickinson, in his law practice. After his father's death, Austin became treasurer of Amherst College from 1873 until his death. In addition to his law practice and treasury work, Dickinson took part in numerous civic projects and responsibilities, such as moderating the town meetings from 1881 until his death, and acting as president of the Village Improvement Association.
Dickinson married Susan Huntington Gilbert, a friend of his sister Emily from childhood, in 1856. They had three children and resided at the Evergreens, which stood next door to the Dickinson Homestead. Aside from his connection to his world famous sister, Emily, Austin is also known for his longtime affair with Mabel Loomis Todd, a young faculty wife who would eventually edit the first few collections of Emily Dickinson's poetry.