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.

After graduating college, he immigrated to the United States and worked in a paper box factory.

Daniel De Leon nominated Petersen to be national secretary a few months before his death in May 1914.

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.