Knight was born in Atlanta on February 9, 1868, to Clara Corinne Daniel and George Walton Knight. He attended the University of Georgia and graduated with honors in 1888. He took the bar in 1889 and practiced law in Macon. Dissatisfied with the legal profession, Knight turned to journalism.
In 1892 Knight returned to Atlanta and became literary editor for the Atlanta Constitution. During this period he became well known in Atlanta as an orator in the style of his cousin Henry W. Grady and often served as master of ceremonies for various events. In 1895 he married Edith M. Nelson of Atlanta, and they eventually had two daughters. In addition to starting a family and establishing his journalistic career, Knight studied Georgia history and served as a lay pastor in the Presbyterian denomination.
Knight left the Atlanta Constitution in 1902 to attend seminary. Upon his departure the Constitution paid tribute to him: “Mr. Knight is one of the most talented young journalists in Georgia. He has made a great reputation as an orator, poet and literary man, and his work as an editorial writer on the Atlanta Constitution is of the highest order.” He enrolled at Princeton Theological Seminary in Princeton, New Jersey, where Woodrow Wilson was one of his instructors, and at the same time he began graduate studies at Princeton University. In 1905 Knight was ordained and began serving as associate pastor at Central Presbyterian Church in Washington, D.C.
The continued stress of an unhappy marriage brought Knight to the verge of a nervous breakdown. Rest was recommended, and during his recovery in 1906, Knight traveled in Europe, alone. After returning home, he lived briefly in California and practiced law. Although he tried to reconcile with his wife, they were divorced in 1909. In spite of this personal turmoil, Knight published his first major work, the two volumes of Reminiscences of Famous Georgians, in 1907 and 1908.
Returning to Atlanta and his journalism career, Knight became associate editor of the Atlanta Georgian in 1908, a post he held until 1910. Leaving journalism behind for the last time, he became literary editor and vice president at the Martin and Hoyt Company, where he edited the Library of Southern Literature series with Joel Chandler Harris (although Harris died before any of the volumes were published). In 1913 Knight was appointed compiler of Georgia state records and began work on volumes 22-26 of Colonial Records; Georgia’s Landmarks, Memorials, and Legends (1913-14), and the six volumes of Standard History of Georgia and Georgians (1917). In 1917 Knight married Rosa Talbot Reid, who shared his interest in history. The couple was active in the Atlanta social scene and lived at Spotswood Hall (1913), which was designed by A. Ten Eyck Brown and renovated in the 1930s by Philip Shutze. Spotswood is listed on the National Register of Historic Places.
Working with state records convinced Knight of the necessity of preserving Georgia’s legislative and state documents. He lobbied with much zeal for a state archives and achieved his goal after a prolonged and heated political battle. Even after he was appointed director of the Georgia Department of Archives and History (later Georgia Archives) in 1918, he had to fend off political enemies who sought to abolish his office. His wife assisted him in organizing the historical papers of Georgia. During his tenure at the state archives, from 1919 through 1924, Knight published the first Statistical Register of Georgia, organized the new department and its holdings, provided proper storage for state records, and left a permanent Georgia archives when he retired in 1925. It was a far cry from the days when valuable papers were used by the janitor to light the furnace in the capitol building. Knight was deservedly named “state historian emeritus for life” upon his retirement in 1925.
Knight received honorary degrees from the University of Georgia and King College of Bristol, Tennessee. He was a fellow of the Royal Society of Arts in London, and a member of Phi Beta Kappa. In addition to poetry and newspaper writing, Knight was the author of more than twenty books, including the biography Woodrow Wilson, the Dreamer and the Dream (1924) . His papers are part of the Henry W. Grady Collection and the Joel Chandler Harris Collection at Emory University.
Knight died of heart failure on November 19, 1933, in Clearwater, Florida, and was buried at Christ Church on St. Simons Island. His obituary appeared on the front page of the Atlanta Constitution, and it noted the passing of “one of the most widely-beloved and popular of the state’s literary personages.” His daughter Mary Lamar Knight followed in her father’s footsteps as a journalist and became one of the first female correspondents for United Press International.