He has been described by the American Jerusalem as "among the most influential Jews in San Francisco—as well as national–civic life, from the middle of the 19th century into the 1930s".

After studying law in San Francisco, he was elected a member of the State Assembly in 1892 and admitted to the bar in January 1894.

Representative Kahn also authored the Kahn Exclusion Act, ultimately enacted as the Alien Exclusion Act, telling Congress that "I submit if the Chinese people themselves would deal honestly with us, and if they resorted less to trickery and duplicity to circumvent our laws, then there would be no need of closing up all possible loopholes in the law with the seemingly severely restrictive measures that the Chinese themselves make necessary.

A well-known playground and adjacent ballpark in San Francisco was named in his honor; in 2018, it was proposed to strip his name from the playground due to the fact that he championed the extension of the Chinese Exclusion Act in 1902 which he justified by stating that the Chinese people were "morally, the most debased people on the face of the earth.

"[3] The Western Jewish History Center, of the Magnes Collection of Jewish Art and Life, in Berkeley, California has a large collection of family papers, documents, correspondence, and photographs relating to Julius Kahn and to his wife, Florence Prag Kahn.