After midshipman service in the cruisers Asama and Soya, and battleships Satsuma and Kongō, he attended Naval Torpedo and Gunnery Schools from 1913–1914.

This was followed by tours in the destroyer Sugi and transport Seito and studies at the Japanese Naval War College.

[3] During the 1920s, Mikawa served as chief navigator on a number of ships, including the battleship Haruna and cruisers Tatsuta, Ikoma, and Aso.

However, after the war Mikawa maintained that based on the available intelligence there was an American carrier task force just south of the island of Guadalcanal, one that would surely launch an airstrike in the morning and inflict heavy loses to his fleet, not to mention that just before he set out he was specifically instructed by chief of IJN general staff Osami Nagano that he should avoid losing ships if possible and there simply wasn't enough time left to both attack the transports and withdraw safety under the cover of darkness.

Admiral Mikawa also stated to the High Command of the IJN that fighting the Americans for the Solomon Islands was simply pouring Japanese soldiers, sailors, airmen, and ships into a "black hole".

[3] In March 1943, the destroyer Akikaze evacuated civilians from the Roman Catholic mission headquarters on Kairiru Island and also a group of missionaries from Wewak.

The ~60 civilians, mostly German missionaries, their servants and dependents (including 3 infants), were then massacred on board the destroyer under orders that came from 8th Fleet HQ.

As commander of the 8th Fleet at the time, Mikawa and his chief of staff Vice Admiral Shinzō Ōnishi are implicated in the war crime.

[6] At 8th Fleet HQ a Lieutenant Shigetoku Kami debriefed the captain of Akikaze after the massacre, he was the only staff officer whose name appeared in the testimony of Japanese witnesses.

[6] However, historian Yuki Tanaka writes that their claims are dubious when contrasted with wartime navy procedures in force when issuing orders.

It was unlikely that communication officers of the 8th Fleet would agree to encrypt and deliver Kami's order to the commander of Akikaze, if it did not bear the countersignatures of Mikawa and Ōnishi.

[8] In the opinion of Captain Albert Klestadt, a member of the investigation, even if the admirals did not issue the orders themselves, they had to accept command responsibility for being unable to prevent war crimes committed by subordinates.