William Strong was born and raised in Connecticut but moved to Pennsylvania, where he started his legal career, following his graduation from Yale. On the basis of a successful law practice, Strong served in Congress for two terms as an anti-slavery Democrat. He returned to private law practice but was elected to the Pennsylvania Supreme Court as a Democrat. He then changed parties.
Strong resigned from his judgeship in 1868 in order to make more money. Strong lost his bid for a Supreme Court appointment when backers of Edwin Stanton, the former secretary of war, mustered majorities in Congress to support the nomination. Grant sent up Stanton who was confirmed. The grim reaper struck just four days later, and Stanton went to his grave a Justice of the Supreme Court who never served. Strong won the prize by default.
Though he was regarded as able and hard-working, Strong never devoted much intellectual capital to constitutional matters. He left the bench while in good health, in part to serve as an example to several infirm justices who refused to give up their seats. Strong took up religious causes in his remaining years.