William Brainerd Spencer (February 5, 1835 – February 12, 1882) was an attorney and politician of the planter class, elected as U.S. Representative from Louisiana in 1876, in a contested election decided in his favor and against the Republican Party candidate. That year the Democratic Party regained control of the Louisiana state legislature. He resigned when appointed in 1877 as Associate Justice of the Louisiana Supreme Court, serving until 1880. After that he resumed the practice of law.