He became Chief of the Foreign Department of the Kwantung Leased Territory in 1930 and Secretary to the Japanese Advisor to the Lytton Commission of the League of Nations.

In 1939 he served briefly as Japanese Envoy Extraordinary and Minister Plenipotentiary to Europe and the United States before returning to Japan.

Sir Robert Craigie, British Ambassador to Japan, later noted that "during his term of office as official 'spokesman' ... he displayed on several occasions open hostility to our attitude as regards Japanese actions in China and he was unpopular amongst the foreign newspaper correspondents owing to his somewhat rough manner and indifferent command of English".

[3] After leading a strike at the Foreign Ministry in 1940, he was sacked as an official spokesman but was appointed roving ambassador to Nazi-occupied Europe.

[5] In July 1941, Time quoted Kawai as saying he was tired of hearing the word "drive" to describe Japan's intentions and that territorial expansion was an old-fashioned phrase.

He was also a guest at The Lodge after Curtin became Prime Minister, and at the opening of the Australian War Memorial in Canberra on 11 November 1941.

He sent a telegram to Curtin expressing his sympathy at the loss of HMAS Sydney on 1 December 1941, only days before Australia declared war on Japan.