His law partner, William M. Malone, was also Chairman of the Democratic Party in California during much of the Roosevelt and Truman administrations.

[7][8] Among Sullivan's notable cases are Serrano v. Priest (1971),[9] in which he addressed the inequality of public school financing.

He also wrote the court's opinion in Castro v. State (1970),[12] which struck down a provision of the California Constitution that disenfranchised citizens who were literate in Spanish but not in the English language.

[13] After stepping down from the bench on January 19, 1977, Sullivan taught for 15 years at the University of California, Hastings College of the Law, retiring in 1993.

[7][14] In 1975, the California Trial Lawyers Association named him appellate judge of the year.