As a pioneer of what was sometimes called "sound poetry", he was also a forerunner of performance art, often working in multimedia before that term was coined. He was a founding member of the neo-Dada art movement Fluxus, he influenced groups including New York's LANGUAGE poets, and also many poets in Britain, including Bob Cobbing.

MacLow was born in Chicago and from the age of four studied music. Despite doing graduate-level work in philosophy and literary criticism at the University of Chicago, he left in 1943 after four years with only a two-year associate degree. He moved to New York, where he lived the rest of his life. He did odd jobs and edited a pacifist-anarchist newsletter, writing music and poetry which bore little resemblance to his later work.

After providing the music for the Living Theatre's production of Auden's Age Of Anxiety in 1954, MacLow changed his life. He enrolled at Brooklyn College and graduated with a degree in Greek in 1958. He then began working as an editor with reference book publishers, and taught in the 1960s at New York University.

Influenced by John Cage's musical theories of systematic chance, he decided performance was the core of poetry; texts constituted a guide for that performance. Biblical Poems (1954-55) was his pivotal work, which applied random performance instructions, based on rolling dice, to Hebrew scripture. Like Cage's work, it included rhythmical sections of silence.

The Marrying Maiden: A Play Of Changes, with music by Cage, was performed by the Living Theatre in 1960. The text, never published, was accompanied by an "action pack" of 1,400 playing cards with a series of "commands", structured on the principle of the I Ching and a random digit table. It aimed to disassemble language and reassemble it in ways that would surprise both MacLow and his listeners or readers. In effect, the rules for everyday language were turned on themselves.

In 1963 MacLow married the painter Iris Lezak. His 400-page Stanzas For Iris Lezak (1972), is one of his most difficult works. He said it was designed to thwart the reader's aim "to reach the is of non-ego". By the time they divorced in 1973, he had written his Odes For Iris, in strict syllabic verse. Some of them appeared in magazines, and in Representative Works (1986), they are the more powerful for their traditional directness.

MacLow's six-act play, Verurious Sanguinaria, first performed in 1967 in Yoko Ono's New York loft, was written by culling random words or phrases, one each from 26 dictionaries and became his only work published by a mainstream press, although one of the six acts was omitted. The complete version was reprinted by the small press Sun & Moon. On the page, MacLow's instructions and notations aimed to give the reader the power to help create the work's meaning each time it was read. Thus, every reading or performance of it is, by definition, unique.

Although his theories seemed overpowering to many, MacLow in performance was immediately accessible and entertaining, while still challenging. His "sources" varied from the Bible and dictionaries to writers such as Kathy Acker and the country singer Ian Tyson. His work incorporated dance choreography with musical notation, and made early use of computers.

His series called Vocabularies used the names of people as the basis for as many partial anagrams as he could fit on to a single sheet of paper. One was written for Anne Tardos, a poet and performance artist. She and MacLow married in 1990. After meeting Tardos, his work shifted again, away from found material to sources he that he wrote himself, most notably in From Pearl Harbor To FDR's Birthday (1982).

In 1985 MacLow was awarded a Guggenheim Fellowship. In 1999 he received the Academy of American Poets' Wallace Stevens award.