Sydney Lanier was born February 3, 1842, in Macon, Georgia, to parents Robert Sampson Lanier and Mary Jane Anderson; he was mostly of English ancestry, with his distant French ancestors having immigrated to England in the 16th century.[1] He began playing the flute at an early age, and his love of that musical instrument continued throughout his life. He attended Oglethorpe University near Milledgeville, Georgia, graduating first in his class shortly before the outbreak of the American Civil War.

He fought in the Civil War, primarily in the tidewater region of Virginia, where he served in the Confederate signal corps. Later, he and his brother Clifford served as pilots aboard English blockade runners. On one of these voyages, his ship was boarded. Refusing to take the advice of the British officers on board to don one of their uniforms and pretend to be one of them, he was captured. He was incarcerated in a military prison at Point Lookout in Maryland, where he contracted tuberculosis (generally known as "consumption" at the time). He suffered greatly from this affliction for the rest of his life.

Shortly after the war, he taught school briefly, then moved to Montgomery, Alabama, where he worked as a desk clerk at The Exchange Hotel and also performed as a musician; he was the regular organist at The First Presbyterian Church in nearby Prattville. He wrote his only novel, Tiger Lilies (1867) while in Alabama. In 1867, he moved to Prattville, at that time a small town just north of Montgomery where he taught and served as principal of a school. He married Mary Day of Macon (1876) that same year and moved back to his hometown and began working in his father's law office. After taking and passing the Georgia bar, he practiced as a lawyer for several years. During this period he wrote a number of poems in the "cracker" and "negro" dialects of his day about poor white and black farmers in the Reconstruction South. He traveled extensively through southern and eastern portions of the United States in search of a cure for his tuberculosis.

While on one such journey in Texas, he rediscovered his native and untutored talent for the flute and decided to travel to the northeast in hopes of finding employment as a musician in an orchestra. Unable to find work in New York, Philadelphia, or Boston, he signed on to play flute for the Peabody Orchestra in Baltimore, Maryland, shortly after its organization. He taught himself musical notation and quickly rose to the position of first flautist. He was famous in his day for his performances of a personal composition for the flute called "Black Birds," which mimics the song of that species.

In an effort to support Mary and their three sons, he also wrote poetry for magazines. His most famous poems were "Corn" (1875), "The Symphony" (1875), "Centennial Meditation" (1876), "The Song of the Chattahoochee" (1877), "The Marshes of Glynn" (1878), and "Sunrise" (1881). The latter two poems are generally considered his greatest works. They are part of an unfinished set of lyrical nature poems known as the "Hymns of the Marshes", which describe the vast, open salt marshes of Glynn County on the coast of Georgia. There is a historical marker in Brunswick commemorating the writing of "The Marshes of Glynn". The largest bridge in Georgia (as of 2005), a short distance from the marker, is named The Sidney Lanier Bridge.

Late in his life, he became a student, lecturer, and, finally, a faculty member at the Johns Hopkins University in Baltimore, specializing in the works of the English novelists, Shakespeare, the Elizabethan sonneteers, Chaucer, and the Anglo-Saxon poets. He published a series of lectures entitled The English Novel (published posthumously in 1883) and a book entitled The Science of English Verse (1880), in which he developed a novel theory exploring the connections between musical notation and meter in poetry.

Putting these theories into practice, he developed a unique style of poetry written in logaoedic dactyl, which was strongly influenced by the works of his beloved Anglo-Saxon poets. He wrote several of his greatest poems in this meter, including "Revenge of Hamish" (1878), "The Marshes of Glynn" and "Sunrise". In Lanier's hands, the logaoedic dactylic meter led to a free-form, almost prose-like style of poetry that was greatly admired by Henry Wadsworth Longfellow, Bayard Taylor, Charlotte Cushman, and other leading poets and critics of the day. A similar poetical meter was independently developed by Gerard Manley Hopkins at about the same time (there is no evidence that they knew each other or that either of them had read any of the other's works).

Lanier also published essays on other literary and musical topics and a notable series of four redactions of literary works about knightly combat and chivalry in modernized language more appealing to the boys of his day:

• The Boy's Froissart (1878), a retelling of Jean Froissart's Froissart's Chronicles, which tell of adventure, battle and custom in medieval England, France and Spain
• The Boy's King Arthur (1880), based on Sir Thomas Malory's compilation of the legends of King Arthur and the Knights of the Round Table
• The Boy's Mabinogion (1881), based on the early Welsh legends of King Arthur, as retold in the Red Book of Hergest.
• The Boy's Percy (published posthumously in 1882), consisting of old ballads of war, adventure and love based on Bishop Thomas Percy's Reliques of Ancient English Poetry.

He also wrote two travelogues that were widely read at the time, entitled Florida: Its Scenery, Climate and History (1875) and Sketches of India (1876) (although he never visited India).Lanier finally succumbed to complications caused by his tuberculosis on September 7, 1881, while convalescing with his family near Lynn, North Carolina. He was only 39. Lanier is buried in Green Mount Cemetery in Baltimore. Baltimore also honored him with a large and elaborate bronze and granite sculptural monument, created by Hans K. Schuler and located on the campus of the Johns Hopkins University.

In addition to the monument at Johns Hopkins, Lanier was also later memorialized on the campus of Duke University in Durham, North Carolina. Upon the construction of the iconic Duke Chapel between 1930 and 1935 on the university's West Campus, a statue of Lanier was included alongside two fellow prominent Southerners, Thomas Jefferson and Robert E. Lee. This statue, which appears to show a Lanier older than the 39 years he actually lived, is situated on the right side of the portico leading into the Chapel narthex. It is prominently featured on the cover of the 2010 autobiographical memoir Hannah's Child, by Stanley Hauerwas, a Methodist theologian teaching at Duke Divinity School.

Lanier's poem "The Marshes of Glynn" is the inspiration for a cantata by the same name that was created by the modern English composer Andrew Downes to celebrate the Royal Opening of the Adrian Boult Hall in Birmingham, England, in 1986.

Several things have been named for Sidney Lanier:

• Lake Lanier, operated by the U.S. Army Corps of Engineers northeast of Atlanta
• Lanier Elementary School in nearby Gainesville, Georgia
• Lanier Elementary School in Tulsa, Oklahoma
• Lanier County, Georgia
• Lake Lanier in Tryon, North Carolina
• Sidney Lanier Bridge over the South Brunswick River in Brunswick, Georgia
• The Sidney Lanier Building (previously Sidney Lanier Elementary School) on the campus of Glynn Academy, in Brunswick, Georgia
• Lanier's Oak, in Brunswick, Georgia
• Lanier Middle Schools in Houston, Texas, Buford, Georgia, and Fairfax, Virginia
• Lanier High Schools in Montgomery, Alabama, Macon, Georgia (destroyed by fire in 1967), Austin and San Antonio, Texas
• Sidney Lanier Elementary School in Tulsa, Oklahoma
• Sidney Lanier School in Gainesville, Florida.
• Lanier Heights Neighborhood, Washington, D.C.
• Sidney Lanier high School in Austin, Texas
• Sidney Lanier High School in San Antonio, Texas
• Sidney Lanier Cottage [2], the birthplace of Lanier, in Macon, Georgia

Lanier, his life, his talent as a flautist, and his poetry all figure prominently in the 1969 science-fiction novel Macroscope by Piers Anthony. Several quotations from "The Marshes of Glynn" and other references appear throughout the novel, and indeed Lanier and his work are central to one of the characters in the story.