Together with Ernst Thälmann of Germany, Maurice Thorez of France, Palmiro Togliatti of Italy, Earl Browder of the United States, and Harry Pollitt of Great Britain, Buck was one of the top leaders of the Joseph Stalin-era Communist International.

On August 11, 1931, the Communist Party offices in Toronto were raided, and Buck and several of his colleagues were arrested and charged with sedition.

[3] In late 1933, Minister of Justice Hugh Guthrie admitted in the House of Commons of Canada that shots had been deliberately fired into Buck's cell but "just to frighten him."

Buck and other prominent communist leaders were forced underground and ultimately into exile in the United States because of their support for the pact between Germany and the Soviet Union, both of which invaded Poland at the start of the Second World War.

There was controversy within the party when a posthumous version of his memoirs was published in 1977 by NC Press based on interviews conducted for the CBC in 1965.

In Yours in the Struggle: Reminiscences of Tim Buck, the former party leader criticized Nikita Khrushchev and was somewhat defensive of Stalin, although not departing from the international Communist movement's current perspective.

[4] Earlier in 1975, Progress Books published Tim Buck — A Conscience for Canada by Oscar Ryan, which is considered to be the party-approved biography.

Canadian Trotskyist Ian Angus also criticized Yours in Struggle with regards to accusations that Buck had stated misinformation with regards to the purging of alternate voices during his early rise in the party.