Kuwayama Sadaharu served as a bushō during the Azuchi-Momoyama and early Edo periods.  He held the title of Junior Fifth Rank (Lower), Master of the Imperial Guards of the Left Division.  Sadaharu had a nephew with the same name (Kuwayama Iga-no-kami Sadaharu).  To distinguish between him and and his nephew, his name is also written as Kuwayama Kodenji or Kuwayama Sakon Taifu.  Katagiri Sadamasa, a daimyō and tea master from the early Edo period, studied under Sadaharu.  Sadaharu’s Buddhist name was Dōun.

Sadaharu was born as the third son of Kuwayama Shigeharu.

First, he served Toyotomi Hidenaga and was granted a fief of 2,500 koku in Yamato Province.  After the death of Hidenaga, he served Toyotomi Hideyoshi.  In 1592, at the Bunroku Campaign, he deployed with his nephew, Kuwayama Kazuharu (the son of Kuwayama Kazushige who was Sadaharu’s older brother).  In this conflict, he commanded naval forces.

Next, he served the Tokugawa clan.  In 1600, at the Battle of Sekigahara, Sadaharu joined the Eastern Army and, together with his brother, Kuwayama Shigeharu, contributed on the battlefield in Wakayama.  In 1615, at the Summer Campaign of the Siege of Ōsaka, he supported the Tokugawa and, at the Battle of Dōmyō Temple, joined Niwa Ujinobu and others in fighting against Susukida Kanesuke.

Sadaharu learned the tea ceremony as a disciple of Sen no Dōan (the eldest son of Sen no Rikyū) and Furuta Oribe.  Sadaharu adopted the name of Sōsen and, in his latter years, endeavored to convey the ceremonial practices of Sen no Rikyū for later generations.

On 7/7 of Kanei 9 (1632), Sadaharu died at the age of seventy-three.