Alfred Joyce Kilmer was born on December 6, 1886, in New Brunswick, New Jersey. He was the youngest child of Annie Ellen Kilburn, a minor writer and composer, and Dr. Frederick Barnett Kilmer, a physician and analytical chemist known for inventing Johnson and Johnson's baby powder. Kilmer was named after two priests from Christ Church in New Brunswick, where his family were parishioners. He attended Rutgers College Grammar School and later pursued higher education at Rutgers College and Columbia University, graduating with a Bachelor of Arts degree in 1908.

Kilmer is best remembered for his poem "Trees," published in 1913, which reflects his appreciation for the beauty of nature and his Catholic faith. He was a prolific poet, journalist, literary critic, editor, and lecturer, contributing to various publications such as the New York Times Sunday Magazine and the Literary Digest. Kilmer's work was often compared to that of British writers G. K. Chesterton and Hilaire Belloc.

In 1917, Kilmer enlisted in the New York National Guard and served in the 69th Infantry Regiment during World War I. He was killed by a sniper's bullet at the Second Battle of the Marne on July 30, 1918, at the age of 31. Kilmer was posthumously awarded the French Croix de Guerre and the Purple Heart Medal. He was married to Aline Murray, with whom he had five children. Despite some criticism of his work as overly sentimental, Kilmer's legacy endures, particularly through his poem "Trees," which continues to be celebrated and anthologized.