William was educated at country state schools and the University of Sydney, where he graduated B.A. with a first class in classics in 1880, M.A. in 1882, LL.B. in 1885 and LL.D. in 1887.
William was educated at country state schools, including Kiama, and the University of Sydney, where he won a scholaship. Cullen graduated B.A. with first class honours in classics in 1880, M.A. in 1882, LL.B. in 1885 and LL.D. in 1887.