In 1872, Yoshihara was a last-minute addition to the Iwakura Mission in the position of Third Secretary. The delegation met with President Ulysses S. Grant, but was unsuccessful in its goal of revising the unequal treaties. He accompanied the Mission on to England and returned to Japan in March 1873.
Japan
On his return to Japan, Yoshihara accepted a post at the Foreign Ministry as First Secretary, and was assigned as a liaison to the American Consulate-General in Japan. The following year, he joined the Ministry of Finance as Director of the Yokohama Customs Office. However, in 1874 at the request of Ōkubo Toshimichi, he joined Gustave Emile Boissonade and the Japanese delegation to Qing dynastyChina in the negotiations leading to the Japanese Expedition of 1874 to Taiwan. He returned to the Ministry of Finance in 1877 as First Secretary and Director of the Customs Bureau.
Paris
In November 1878, Yoshihara accompanied Matsukata Masayoshi and Aoki Shuzo to Paris in another unsuccessful attempt at revision of the unequal treaties. On February 28, 1880, he was made a director of the Yokohama Specie Bank and also held the post of Vice-Finance Minister. With the creation of the Bank of Japan, per the recommendation of Matsukata Masayoshi, Yoshihara was selected as the 1st Governor of the Bank of Japan on October 6, 1882.