Joseph Katz worked for Soviet intelligence from the 1930s to the late 1940s as one of its most active liaison agents. Katz was assigned management of the “First Line,” that part of the NKGB mission aimed at recruiting selected members of the CPUSA. He was an agent/group leader (gruppovik) and co-owner of a Soviet front company that manufactured gloves.
The Venona project suggests he may have been implicated, along with Amadeo Sabatini, in the murder of Walter Krivitsky in 1941. After Jacob Golos death in November 1943, spotting and recruitment was taken over by Katz by mid–1944, while Elizabeth Bentley continued as manager and courier. Katz was extremely active at this time. Katz was known to Elizabeth Bentley as “Jack.”
In 1944 Katz was put in charge of handling agent recruitments from the New York TASS office headed by Vladimir Pravdin, former Rezident of the NKGB in New York. And in September 1944 Katz was freed of other liaisons (operations) and was assigned to work directly under Washington D.C. Rezident Anatoli Gorsky. Gorsky came to the United States to implement a new security program of isolating agents from each other by a complicated arrangement of cutouts.
Katz was to arrange a meeting between one "Margarita and a new person" in mid-October 1944. Katz had been meeting "Margarita" for some time but had made no attempt to recruit her because she was causing the KGB anguish by equating Stalinism and Nazism and, therefore, was not judged to be a reasonable risk nor a cooperative worker. At that time it was decided only to keep an eye on her. Margarita continued to be of considerable concern to KGB Moscow. On 6 October 1944, New York cabled its awareness of the problem, probably in answer to headquarters insistence on further information, stating that, according to Katz, she was hostile to "our firm but not the country." She evidently explained to Katz "her hostile frame of mind and her simultaneous desire to return home." The New York Resident was not about to meet her personally, and informed Moscow that "there are no grounds for not trusting Katz' conclusions which were being passed on." 
Katz and Bentley’s operations in New York and Washington were very extensive. Bentley would eventually name more than 80 individuals who were providing information to the Soviet intelligence from a dozen government institutions.
Katz informed Bentley at their first meeting in October 1944 that Gorsky had been sent to the United States to improve security of NKGB operations. One aspect of this modernization was to have Bentley turn over to NKGB control all of her agents not previously surrendered to NKGB officers.
After Bentley's defection Katz was assigned the task of killing her, but the murder was never carried out. Katz moved to Western Europe to form a company for covering the illegal courier line between Europe and U.S. Katz lived in France from 1948 to 1951 then moved to Israel. His code names in the Venona project are "X" and "Informer".
- Venona 1337 New York to Moscow, 19 September 1944.
- Venona 1411 New York to Moscow, 6 October 1944.
- Haynes, John Earl & Klehr, Harvey, Venona: Decoding Soviet Espionage in America, (Yale University Press, 2000). ISBN 0300084625.
- Allen Weinstein and Alexander Vassiliev, The Haunted Wood: Soviet Espionage in America--the Stalin Era (New York: Random House, 1999).
- Bernard Schuster and Joseph Katz: KGB Master Spies in the United States