This article is about the Associate Justice of the U.S. Supreme Court; for Justice Lamar's father of the same name who was a Georgia lawyer and state court judge, see Lucius Quintus Cincinnatus Lamar (I).

Lucius Quintus Cincinnatus Lamar (September 17,1825–January 23, 1893) was a native Georgian who graduated from Emory College (later Emory University) in 1845, and married the daughter of Augustus Baldwin Longstreet, one of the school's early presidents.

Lamar would go on to represent Mississippi in the United States Senate from 1877 to 1885 and, later, become the lone Mississippian to serve on the Supreme Court of the United States, 1888 to 1893. Lamar had served as United States Secretary of the Interior under President Grover Cleveland from March 6, 1885 to January 10, 1888.

Three U.S. counties are named in his honor: Lamar County, Alabama; Lamar County, Georgia; and Lamar County, Mississippi.

|- style="text-align: center;" | width="30%" |Preceded by:
William Burnham Woods | width="40%" style="text-align: center;" |Associate Justice of the Supreme Court of the United States
1888–1893 | width="30%" |Succeeded by:
Howell Edmunds Jackson