From the late 1940s until 1974, Moondog lived as a street musician and poet in New York City, busking mostly on 53rd Street and 6th Avenue in Manhattan. In addition to his music and poetry, he was also known for the distinctive Viking garb that he wore, which included a horned helmet. He partially supported himself by selling copies of his poetry and his musical philosophy. Because of his street post's proximity to the famed 52nd Street nightclub strip, he was well-known to many jazz musicians and fans.
Moondog's early work was championed by Artur Rodzinski, the conductor of New York Philharmonic in the '40s. He released a number of 78s, 45s and EPs of his music in the 1950s, as well as several LPs on a number of notable jazz labels, including an unusual record of stories for children with actress Julie Andrews in 1957. For ten years no new recordings were heard from Moondog until producer James William Guercio took him into the studio to record an album for Columbia Records in 1969.
The track "Stamping Ground", with its odd preamble of Moondog saying one of his epigrams, was featured on the sampler double album Fill Your Head with Rock (CBS, 1970). The melody from the track "Bird's Lament (In memory of Charlie Parker)" was later sampled by Mr. Scruff as the basis for his song "Get a Move On", which was then used in commercials for the Lincoln Navigator SUV.
A second album produced with Guercio featured Moondog's daughter as a vocalist and contained song compositions in canons and rounds. The album did not make as large an impression in popular music as the first had. The two CBS albums were re-released as a single CD in 1989.
The English pop group Prefab Sprout included the song 'Moondog' on their seminal album Jordan: The Comeback released in 1990 as a tribute to Hardin.
In a search for new sounds, Moondog also invented several musical instruments, such as the "Oo", a small triangular shaped harp, the "Ooo-ya-tsu", and the "Trimba", a triangular percussion instrument invented in the late 40s. The Original Trimba today is still played by Stefan Lakatos, Swedish percussionist, close friend and pupil of Moondog, who Moondog had taught how to build the instrument.
Moondog had an idealised view of Germany ("The Holy Land with the Holy River" — the Rhine), where he settled in 1974. A young German student named Ilona Goebel hosted him, first in Oer-Erkenschwick, and later on in Münster in Westphalia, Germany, where he spent the remainder of his life.
Moondog visited America briefly in 1989, for a tribute in which Phillip Glass himself asked him to conduct the Brooklyn Philharmonic Chamber Orchestra, at the New Music America Festival in Brooklyn, stimulating a renewed interest in his music.
He recorded many albums, and toured both in the US and in Europe — France, Germany and Sweden.