Reverdy Johnson was born in 1796 in Annapolis, Maryland. He graduated from St. John's College (Annapolis) in 1811, studied the law, was admitted to the state bar in 1816, and became a noted lawyer in Baltimore. Johnson also entered politics, serving in the Maryland state legislature in 1821 and again in 1826.

Johnson continued to practice the law until he was elected to the United States Senate as a Whig in 1844. He then left the Senate in 1849 to become President Zachary Taylor's attorney general, a post he held until Taylor's death in 1850. After leaving office, Johnson resumed his practice of the law, representing the slaveowner in the Dred Scott Supreme Court case. Though sympathetic to the Southern cause, he served as a delegate to the 1861 peace conference and, as a member of the Maryland House of Representatives, urged state leaders not to secede from the Union, regarding the act as a form of treason.

In 1862, Johnson was elected to the United States Senate as a Democrat and served until 1868, when he resigned to become the American minister to Great Britain; he held that post until 1869. Upon his return to the United States, Reverdy Johnson resumed his legal career and continued to practice until his death in 1876.