He was born in New York City to Hermann and Louisa Kreymborg, who ran a small cigar store, and he spent most of his life there and in New Jersey. He was an active figure in Greenwich Village and frequented the Liberal Club.
He was the first literary figure to be included in Alfred Stieglitz's 291 circle, and was briefly associated with the Ferrer Center where Man Ray was studying under Robert Henri. From 1913 to 1914, Kreymborg and Man Ray worked together to bring out ten issues of the first of Kreymborg's prominent modernist magazines: The Glebe. Ezra Pound — who had heard about The Glebe from Kreymborg's friend John Cournos — sent Kreymborg the manuscript of Des Imagistes in the summer of 1913 and this famous first anthology of Imagism was published as the fifth issue of The Glebe
In 1913 Man Ray and Samuel Halpert, another of Henri's students, started an artist's colony in Ridgefield, New Jersey. This colony was often also referred to as 'Grantwood' and comprised a number of clapboard shacks on a bluff. Kreymborg moved to Ridgefield and launched Others: A Magazine of the New Verse with Skipwith Cannell, Wallace Stevens, and William Carlos Williams in 1915. Pound had, along with the Des Imagistes poems, written to Kreymborg suggesting that he contact 'old Bull' Williams, that is William Carlos Williams. Williams did not live far from Ridgefield, and he became involved in the magazine. Soon there was a group of artists associated with the magazine. Marianne Moore came to Ridgefield for picnics, and in 1915 Marcel Duchamp moved in. Regarding Marianne Moore, she was asked in an interview whether Alfred Kreymborg was her American discoverer, to which she replied, "It could be said, perhaps; he did all he could to promote me. Miss Monroe and the Aldingtons had asked me simultaneously to contribute to Poetry and The Egoist in 1915. Alfred Kreymborg was not inhibited. I was a little different from the others. He thought that I might pass as a novelty, I guess.
1915 also saw the publication of a story in part based on a personal experience. The story was titled 'Edna' and published as Edna: The Girl of the Street; by the Greenwich Village entrepreneur Guido Bruno; the subtitle was Bruno's idea, added without the consent of the author. John Sumner of the New York Society for the Suppression of Vice raised a stir; there was a court case which led to the Bruno's imprisonment. The attendant morals row drew in George Bernard Shaw and Frank Harris: Harris made an impassioned statement in court defending the publisher.
Kreymborg was life-long friends with Carl Sandburg, each indepentently choosing to write in free verse. Kreymborg's tone-poems, or 'mushrooms', had seldom made it into print, but in 1916, soon after his move to Ridgefield they were brought out in book form by John Marshall as 'Mushrooms: A Book of Free Forms' and Williams praised them as a "triumph for America".
Kreymborg continued to edit Others somewhat erratically until 1919; he then in June 1921 sailed to Europe to act as co-editor of Broom, An International Magazine of the Arts (along with Harold Loeb). Contributors included Malcolm Cowley, E. E. Cummings, Amy Lowell and Walter de la Mare. The magazine lost money. Kreymborg soon resigned and the magazine ceased publication in 1924. An ironic anecdote on the status of modernism: Kreymborg arranged for an aspiring artist Fernand Léger to create the artwork for the cover of volume 2, number 4 of Broom. When Broom ceased publication, the original painting was left behind for its next tenants. Original works by Léger from that time period have sold for several million dollars.
Kreymborg's poems appeared in The Dial in 1923.
In the summer of 1925, Kreymborg was staying in Lake George Village, and happened to meet Paul Rosenfeld who was staying with Stieglitz. In one late night discussion Kreymborg and Rosenfeld lamented the disappearance of various literary magazines, including Broom. Another neighbour, Samuel Ornitz appeared and offered financial backing for an annual book of new writing. Thus Kreymborg and Rosenfeld founded American Caravan, which was to be edited by Lewis Mumford and Van Wyck Brooks. The Second American Caravan, was edited by Kreymborg, Mumford, and Rosenfeld; it was reviewed the December 1928 issue of The Dial
1925 also saw the publication of his autobiography Troubador, in which he refers to himself in the third person by the nicknames 'Ollie' and 'Krimmie'. The books also describes his first unsuccessful marriage to a girl called Maude, and then his second marriage to Dorothy ("Dot") Bloom.
Kreymborg maintained a long-term connection with Alfred Stieglitz primarily because of Kreymborg's relationship with Hugo Knudsen, who invented some of the early photo-printing processes that Stieglitz utilized. Knudsen and Kreymborg both married sisters Beatrice (Bea) and Dot Bloom (respectively).
He also wrote puppet plays (his most famous being Manikin Minikin and Lima Beans), which he performed with his wife, Dot, while touring the United States.
Kreymborg played chess at a professional standard, on two occasions he played and lost to Jose Capablanca, including a defeat in 1910 due to a mix-up in his end-game He drew one game with the U.S. Champion Frank Marshall in the 1911 Masters Tournament, but shortly afterward left the chess world after a stunning defeat by Oscar Chajes, returning to the sport roughly twenty-three years later. He wrote the article 'Chess Reclaims a Devotee', which is well-known in chess circles.
Kreymborg was very close with "Sandy" Calder.
Due to his knack of "discovering" and publishing some of the most important poets during his time, Kreymborg later became president of the American Society of Composers, Artists, and Performers.
Kreymborg later became a relatively conservative poet, but — according to Julian Symons — "never an interesting one
In Namedropping, Richard Ellmann writes a short chapter about a meeting with Kreymborg in the early 1960s.