Born in New York, Seeger moved with his family to Staten Island at the age of one and remained there until the age of ten. In 1900, his family moved to Mexico for two years, which influenced the imagery of some of his poetry. His brother Charles Seeger, a noted musicologist, was the father of the American folk singer, Pete Seeger.

Seeger entered Harvard in 1906 after attending several elite preparatory schools, including Hackley School. At Harvard, he edited and wrote for the Harvard Monthly. After graduating in 1910, he moved to Greenwich Village for two years, where he wrote poetry and enjoyed the life of a young bohemian.

During that time, he attended soirées at the Mlles. Petitpas' boardinghouse (319 West 29th Street), where the presiding genius was the artist and sage John Butler Yeats, father of the poet.

Having moved to the Latin Quarter of Paris to continue his seemingly itinerant intellectual lifestyle, on August 24, 1914, Seeger joined the French Foreign Legion so that he could fight for the Allies in World War I (the United States did not enter the war until 1917). He was killed in action at Belloy-en-Santerre, famously cheering on his fellow soldiers in a successful charge after being hit several times himself by machine gun fire. One of his more famous poems, I Have a Rendezvous with Death, was published posthumously. Indeed, a recurrent theme in both his poetic works and his personal writings prior to falling in battle was his desire for his life to end gloriously at an early age.

Seeger's poetry was not published until 1917, a year after his death. Poems, a collection of his works, was relatively unsuccessful, due, according to Eric Homberger, to its lofty idealism and language, qualities out of fashion in the early decades of the twentieth century.

Poems was reviewed in The Egoist, where the critic...T. S. Eliot, Seeger's classmate at Harvard...commented that,

"Seeger was serious about his work and spent pains over it. The work is well done, and so much out of date as to be almost a positive quality. It is high-flown, heavily decorated and solemn, but its solemnity is thorough going, not a mere literary formality. Alan Seeger, as one who knew him can attest, lived his whole life on this plane, with impeccable poetic dignity; everything about him was in keeping."

On 4 July 1923, the President of the French Council of State, Raymond Poincaré, dedicated a monument in the Place des États-Unis to the Americans who had volunteered to fight in World War I in the service of France. The monument, in the form of a bronze statue on a plinth, executed by Jean Boucher, had been financed through a public subscription.

Boucher had used a photograph of Seeger as his inspiration, and Seeger's name can be found, among those of twenty-three others who had fallen in the ranks of the French Foreign Legion, on the back of the plinth. Also, on either side of the base of the statue, are two excerpts from Seeger's "Ode in Memory of the American Volunteers Fallen for France", a poem written shortly before his death on 4 July 1916. Seeger intended that his words should be read in Paris on 30 May of that year, at an observance of the American holiday, Decoration Day (later known as Memorial Day):

They did not pursue worldly rewards; they wanted nothing more than to live without regret, brothers pledged to the honor implicit in living one's own life and dying one's own death. Hail, brothers! Goodbye to you, the exalted dead! To you, we owe two debts of gratitude forever: the glory of having died for France, and the homage due to you in our memories.

"I Have a Rendezvous with Death" was one of President John F. Kennedy's favorite poems. His wife Jacqueline memorized it and would often recite it upon his request.

In the 1993 film In the Line of Fire, the assassin Mitch Leary (played by John Malkovich) cites I Have a Rendezvous with Death as President Kennedy's favorite, and says that it is "not a good poem."

A shortened form of Seeger's poem I Have a Rendezvous with Death was featured in the Joseph Kosinski-directed trailer for the video game Gears of War 2 that debuted during E3 2008.

Actor Darren McGavin joined The First Poetry Quartet, to recite a very effective version of poem I Have a Rendezvous with Death in The Men Who Marched Away presented on PBS.