Born to a samurai family in the Satsuma Domain (present-day Kagoshima Prefecture), Kamimura served as a foot soldier during the Boshin War.

After the outbreak of the First Sino-Japanese War the following year, Kamimura was given command of the new cruiser Akitsushima, winning distinction at the Battle of the Yalu River on 17 September 1894.

In the years following the war, Kamimura held a series of posts in the Navy Ministry as well as staff and fleet commands until his promotion to vice admiral in 1903.

Placed in command of the IJN 2nd Fleet following the first months of the Russo-Japanese War, Kamimura was ordered to contain the Russian cruiser squadron based in Vladivostok.

After the Russians escaped and sank Japanese troopships in the Sea of Japan (April and June 1904), he became the object of widespread popular dissatisfaction, with a mob attacking his Tokyo residence, and newspapers hinting that he should commit suicide.