During his period in the United Kingdom and in the Foreign Ministry, he helped lay the foundations for the Anglo-Japanese Alliance, which was concluded in 1902.

In doing so he was not simply outflanking the extremists opposed to him; he was also honouring his own belief that Japan should be a great power like those of Europe."

Katō's decision that Japan should enter World War I greatly angered the genrō, who had not been consulted, and who therefore felt that their power and authority were being slighted.

In 1925, Katō had the General Election Law enacted, which extended the vote to all male citizens over the age of 25.

He also ratified the Peace Preservation Law, which suppressed leftist political organizations, and concluded the Soviet–Japanese Basic Convention.

Katō strove to reduce government spending, but also suffered considerable personal criticism for his family links with Mitsubishi.