[1] He was educated at Norwich Free Academy,[2] then studied abroad, and later graduated from Harvard College in 1881.

He studied art history under Charles Eliot Norton, and after graduating, Slater went on to acquire a notable art collection, including works by Rembrandt, and eventually began lending his paintings to the Slater Museum.

[4] In 1900 Slater sold the village of Slatersville, Rhode Island and the mill within it to James Hooper.

[6] He was survived by his wife Ellen and two children – William A. Slater, Jr. of Norwich and Eleanor Halsey Malone of New York.

[7] After his death, Slater's family sold the remaining Jewett City Mills.