He originally practiced Ryousei Shinkage Ryu under Naitou Sakubee. In Edo, he studied Shintou Munen Ryu under Saitou Yakurou. It is unknown if he ever obtained a teaching license, though his swordsmanship was highly praised.

Early Years/Family:
His childhood name was "Eitarou." He was born on January 24, 1841 (lunar calendar date?) into a lower-class Choshu samurai family, the first son and eldest child of common foot soldier Yoshida Seinai and his wife Iku. (Seinai had been adopted into Iku's family, thus the last name, which he otherwise would not have been allowed. Eitarou himself used the name Yoshida until it was officially granted him in 1863.) Eitarou also had a younger sister named Fusa, who according to one source was eleven years his junior. Ito Hirobumi, who later became the first Prime Minister of Japan, was a childhood friend.

In one letter Yoshida stated that since he was prepared to die for the cause, he wished for his parents to allow Fusa to inherit in his place. It is probably for that reason that he stated elsewhere that he had no intentions of marrying. (However, as he also mentions in letters playing around in the Kyoto Shimabara, it is quite likely that he was involved with one or more women.)

School Years:
He started out in Kubo Gorouzaemon's private school (the predecessor of Yoshida Shoin's Shoka Sonjuku) at age eight, alongside Ito Hirobumi (at the time Shunsuke).

It was said he lived next door to the Shoin family home, and hence started early in his education.*

Among the 70-80 students there, Eitarou and Shunsuke were said to have been the most distinguished. At twelve Yoshida took a break from his studies and went to Edo to serve in the Choshu clan residence there. The next year, he witnessed the arrival of U.S. warships before returning home in the spring to train in various weaponry (guns, swords, spears). He also studied arithmetic with Tahara Seisuke in Kubo's school. In the autumn of 1855 he returned to Edo for a few months before going back home again in February (lunar calendar) of the following year. In November of the same year he met Yoshida Shoin (no relation) for the first time through Masuno Tokumin's introduction and joined Shoin's "Village School Under the Pines", Shoka Sonjuku. Together with Takasugi Shinsaku and Kusaka Genzui, he became known as one of the "Three Musketeers of Shoin" (more literally something like "three handsome disciples under Shoin's tutelage," with "handsome" carrying connotations of "estimable, worthy".) After the arrival of Irie Kuichi, the four of them became the Sonmon Shitennou, or the Big Four of Shoka Sonjuku.

The three fellow students Yoshida grew closest to during this period, however, seem to be Irie (who Yoshida is thought to have been acquainted with before his joining Shoin's school), Nomura Wasaku, and Shinigawa Yajirou (who held so much admiration for Toshimaro that after the Restoration he said that if Yoshida had survived, he would have become Prime Minister).