Promoted to lieutenant on September 26, 1903, he served on a large number of ships, including the gunboat Maya, corvette Kongō, and cruiser Tokiwa.

However, only a month later, he was reassigned to the Imperial Japanese Navy General Staff, joining Japan's delegation to the Versailles Peace Treaty Conference.

A few months later in April 1932, a Korean independence activist named Yun Bong-gil threw a bomb at Japanese dignitaries including Nomura while they were attending a celebration of Emperor Hirohito's birthday at Shanghai's Hongkou Park.

From 1933 to 1937, Nomura served as Naval Councilor on the Supreme War Council, and retired from active service in 1937.

On November 27, 1940, Nomura was sent as ambassador to the United States, replacing Kensuke Horinouchi, who had served since March 1939.

Nomura's repeated pleas to his superiors to offer the Americans meaningful concessions were rejected by his government, while Hull and his boss Roosevelt were far from yielding themselves.

[6] Nomura and Kurusu had to decode the radioed message of Japan's breaking off of the negotiations with the United States, which practically meant war.

While the Japanese Consulate struggled to decipher their own code, Washington had broken it and Hull knew how Nomura was being used by Tokyo as a convenient time-buying ploy.

He continued to serve in an unofficial capacity as an advisor to the government through World War II, and he was appointed to the Privy Council in May 1945.

In the late 1950s, he was considered to be a strong candidate to head the Defense Agency by two prime ministers, Ichirō Hatoyama and Nobusuke Kishi, however he declined both offers and expressed his belief in civilian control of armed forces.

Nomura had been a civilian for nearly two decades by that time, but was still regarded by many as a retired admiral of the old Imperial Japanese Navy.