Lamar was born to a prominent Georgia political family in 1825. He graduated from Emory University in 1845, studied law afterwards and then passed the bar exam in 1847. He laid the foundation for his political career in the ensuing years before the Civil War by becoming involved in the Southern Rights Party and other activities. He was elected U.S. Congressman in 1857 and resigned upon the start of the war.
After the war, Lamar called for reconciliation between the North and the South, earning wide acclaim on both sides. He believed the South could handle its own affairs without intervention from the North. This included that he did not support legislation to give African Americans more freedoms; he was thus an advocate of restoring white rule in the South. Lamar would become the first American politician to serve in the House, Senate, Supreme Court, and Cabinet.