Sakuma Yasumasa served as a bushō and daimyō from the Sengoku to early Edo periods.  He was the lord of the Ōmi-Takashima domain and, later, the Shinano-Iiyama domain.

In 1555, Yasumasa was born as the second son of Sakuma Moritsugu, a bushō serving the Oda clan in Owari Province.

Initially, Yasumasa became the adopted son-in-law of Yasuda Tomomune, a retainer of the Hatakeyama clan who served as the military governors of Kii and Kawachi provinces.  He first adopted the name of Yasuda Hisaroku and later changed to Kyūemon.

After the Hatakeyama clan fell into ruin, Yasumasa, along with his adoptive father, and his older and younger brothers, served Oda Nobunaga.  In the beginning, he was affiliated with Sakuma Nobumori and participated in attacks against the Ishiyama-Hongan Temple.  Later, he served under Shibata Katsuie.  In the sixth month of 1582, Oda Nobunaga died unexpectedly in a coup d’état led by one of his senior retainers, Akechi Mitsuhide, in an event known as the Honnō Temple Incident.  This led to divisions among his senior retainers regarding the successor to Nobunaga.  In 1583, at the Battle of Shizugatake, Yasumasa, together with family members and his adoptive father, joined a battalion led by Sakuma Morimasa to fight against the Hashiba army led by Hashiba Hideyoshi (later known as Toyotomi Hideyoshi).  Yasumasa served with the vanguard forces in battles against Nakagawa Kiyohide in the environs of Lake Yogo.  After Kiyohide fell in battle, Morimasa ordered Kuwayama Shigeharu who was in charge of defending the fortress at Shizugatake to surrender and vacate the premises.  Shigeharu responded that he would not resist but that he wanted Morimasa to wait until after sunset so the fall of the fortress appeared near at hand.

Soon thereafter, reinforcements led by Niwa Nagahide came ashore after crossing Lake Biwa by boat.  These forces converged with the Kuwayama battalion that was supposed to depart from the fortress from around sunset.  Together, these combined forces launched an attack so Morimasa failed to secure the fortress.  Having waited for this opportunity and prepared in advance, Hideyoshi returned with the Hashiba army to the battlefield.  This is known as the Great Return from Mino during which the Hashiba army marched from Ōgaki in Mino to Kinomoto in Ōmi (approximately 52 kilometers) in five hours.  Fierce fighting by the forces from Hideyoshi’s main division later gave rise to the recognition of a group of bushō known as the Seven Spears of Shizugatake.  Meanwhile, the battalion led by Maeda Toshiie and others withdrew so communications were severed between Masamori’s battalion and Katsuie’s main base.  In the end, at the Battle of Shizugatake, the Shibata army suffered a major defeat at the hands of the Hashiba army while Morimasa attempted to flee for his own safety to Kaga in a bid for a later revival but was captured and later executed by Hideyoshi in Kyōto.  Yasumasa’s adoptive father was killed in action.  After the death of Katsuie, Yasumasa and his younger brother, Sakuma Katsuyuki, fled to the landholdings of the Yasuda clan in Kii Province.

At the Battle of Komaki-Nagakute, Yasumasa, together with the Saika Group and the Negoro Group of Kii, affiliated with the combined forces of Tokugawa Ieyasu and Oda Nobukatsu.  Yasumasa fought repeatedly against Nakamura Kazuuji who defended Kishiwada Castle on the side of the Hashiba.  After Hideyoshi settled with Ieyasu and Nobukatsu, Hideyoshi launched a second expedition to Kishū (Kii) and eliminated all opposition elements, including the Saika and Negoro groups, in the province.

Yasumasa and his brother were persuaded by Ieyasu to enter into service for the Odawara-Hōjō clan in the Kantō.  At this time, Yasumasa divorced his wife.  Later, he wed the daughter of a noble named Kajūji Harutomo who served as an intermediary for communications between Emperor Ōgimachi and the military families.  The Conquest of Odawara led by Toyotomi Hideyoshi resulted in the decimation of the Hōjō clan.  Thereafter, Yasumasa and Katsuyuki went underground in the countryside for a while.  Then, through the offices of Okuyama Moriaki (their uncle and a direct retainer of Hideyoshi), the siblings were pardoned by Hideyoshi, reverted from the Yasuda clan to the Sakuma clan, and served Gamō Ujisato.  Yasumasa held land in Oguni in Dewa Province and, in 1590, contributed to suppressing the Kasai-Ōsaki Uprising, a revolt by former retainers of these clans against new landlords appointed by the Toyotomi.  After the death of Ujisato, Yasumasa became a direct retainer of Hideyoshi and was awarded Makishima Castle in Shinano Province.

In 1598, after the death of Hideyoshi, the gobugyō, or Five Commissioners, asked for input from Tokugawa Ieyasu whereupon Yasumasa was granted 7,000 koku in Ogawa in Ōmi Province.

In 1600, at the Battle of Sekigahara, Yasumasa joined the Eastern Army and, owing to his contributions, received an increase to his fief in the Takashima District of Ōmi Province, totaling 15,000 koku and attaining the status of a daimyō.  In 1607, when moving to Edo Castle, his fief was increased by 5,000 koku in Oda in Hitachi Province so his total reached 20,000 koku.  In 1615, for his efforts during the Siege of Ōsaka, he received a further increase of 10,000 koku in Iiyama in Shinano Province for a total fief of 30,000 koku.  Yasumasa then founded the Iiyama domain of the Sakuma family.  In 1617, he was appointed as a member of the otogishū, or retinue of veteran bushō accompanying Tokugawa Kiyohide.

In 1627, Yasumasa died in Edo.  The family temples are the Bangaku Temple in the city of Takashima in Shiga Prefecture and the Daishō Temple in the city of Iiyama in Nagano Prefecture.  His grave is at the Kōgaku Temple in Nihonenoki.  There are graves of the Iiyama and Sakuma families in a temple deep in Mount Kōya and numerous memorial sites.  In the Heisei era, new Buddhist mortuary tablets were made at the Daishō and Keisō temples in Iiyama in Nagano.