Throughout his life, Mattick continually criticised Bolshevism, Vladimir Lenin and Leninist organisational methods, describing their political legacy as "serving as a mere ideology to justify the rise of modified capitalist (state-capitalist) systems, which were [...] controlled by way of an authoritarian state".

[3] With the continuing decline of radical mass struggle and revolutionary hopes, especially after 1923, and having been unemployed for a number of years, Mattick emigrated to the United States in 1926, whilst still maintaining contacts with the KAPD and the AAUE in Germany.

From this time, Mattick focused on Marx's theory of capitalist development and its inner logic of contradictions inevitably growing to crisis as the foundation of all political thoughts within the workers' movement.

Mattick participated in their meetings and contributed to their party publications for several years, during which he also sometimes spoke in the nighttime lecture series at the bohemian Dil Pickle Club, an IWW hangout.

[4] In 1931, under the sponsorship of a local federation of German-speaking socialist clubs and sports groups, he took over as editor of the defunct German-language Chicagoer Arbeiter-Zeitung, a newspaper steeped in radical tradition and at one time edited by August Spies and Joseph Dietzgen.

However, the golden age of the Wobblies' militant strikes had already passed by the beginning of the thirties, and only the emerging unemployed movement again gave the IWW a brief regional development.

In 1933, Paul Mattick drafted a programme for the IWW trying to give the Wobblies a more solid 'Marxist' foundation based on Grossman's theory, although it did not improve the organization's condition.

Among the few willing to offer regular contributions was Karl Korsch, with whom Mattick had come into contact in 1935 and who remained a personal friend for many years from the time of his emigration to the United States at the end of 1936.

From the forties and up through the fifties, Mattick went through a study of John Maynard Keynes and compiled a series of critical notes and articles against Keynesian theory and practice.

Here, he held lectures on Marx' critique of political economy, on the history of the workers movement and served as critical co-referent at seminars with other guests such as Maximilien Rubel, Ernest Mandel, Joan Robinson and others.