| Arnold Petersen | |
| Term Start: | February 1, 1914 |
| Term End: | 1969 |
| Successor: | Nathan Karp |
| Birth Date: | April 16, 1885 |
| Birth Place: | Odense, Denmark |
| Children: | 1 |
Arnold Petersen (April 16, 1885 – February 5, 1976) was the National Secretary of the Socialist Labor Party of America from 1914 to 1969. Petersen played a major role as spokesman for that party and as a promoter of the De Leonist version of Marxist theory in the 20th century.
Arnold Petersen was born in Odense, Denmark, the son of a tailor. After graduating college, he immigrated to the United States and worked in a paper box factory. In 1907, he joined the Socialist Labor Party.
Daniel De Leon nominated Petersen to be national secretary a few months before his death in May 1914. As national secretary, Petersen restructured the party and saved it from bankruptcy. He was also a prolific author, writing over fifty books, including a series of biographical monographs on De Leon, collected as Daniel De Leon: Social Architect.
When he retired as Socialist Labor Party of America leader in 1969, he had been the organizations leader for fifty five of the organization's ninety-four years of existence, and seventy-nine years as a "De Leonist" organization (which the party dates from 1890).
A longtime resident of Teaneck, New Jersey, he died on February 5, 1976, in Paterson, New Jersey.[1]