Mōri Motoaki served as a bushō during the Sengoku and Azuchi-Momoyama periods.  He was a retainer of the Mōri clan.  He had the common name of Shōjūrō.  Motoaki held the official title of gyōbu-taifu, or Vice Minister of Justice.

In 1552, Motoaki was born as the fifth son of Mōri Motonari, the sengoku daimyō based in Aki Province.  His mother was a consort from the Miyoshi clan, a kokujin, or provincial landowner, in Bungo Province.

Suginomori Takayasu, a kokujin from Suō Province who made significant contributions during the Subjugation of Bōchō (meaning Suō and Nagato provinces) by the Mōri army from 1556, did not have a natural heir so, upon orders of Motonari, Motoaki was adopted by the Suginomori as the designated successor of Takayasu.

In 1566, Amago Yoshihisa, the lord of the Amago clan based in Gassantoda Castle, surrendered to the Mōri whereupon senior retainers of the Mōri, Fukubara Sadatoshi and Kuchiba Michiyoshi were initially assigned to guard the castle.  After a period, Motonari appointed Amano Takashige, the commander-in-charge of Matsuyama Castle in the Miyako District of Buzen Province, to serve as the commander-in-charge of Gassantoda Castle.  Takashige, however, firmly refused taking on this major responsibility, and requested that Motoaki serve as the commander-in-charge while he would serve as his deputy.  At this time, Motoaki was only fifteen years old, so Motonari insisted that Takashige serve as the commander-in-charge.  Takashige finally accepted the appointment after Motonari accepted three of his conditions.

On 6/10 of Eiroku 11 (1568), Motoaki was requested to guard Gassantoda Castle and awarded 3,500 kan in Izumo Province.  On 6/12, he submitted a written oath, pledging allegiance to the Mōri clan and promising to render his best efforts.  In addition, he demanded that Mōri Terumoto show mercy toward him.  Before long, however, the Mōri army deployed to Kyūshū (for the Siege of Tachibana Castle and the Battle of Tatarahama) so Motoaki’s assignment to Gassantoda Castle was postponed.

Seeking to take advantage at the absence of the main division of the Mōri army from the Chūgoku Region, beginning in 1569 and continuing into 1570, Yamanaka Yukimori and Amago Katsuhisa invaded Izumo Province with the aim of reviving the Amago family and recapturing the province.  This period also witnessed the Revolt of Ōuchi Teruhiro.  Confronted with an attack on Gassantoda Castle by the Amago revival army, Amano Takashige holed-up in the castle with a small garrison to resist the Amago and, on 11/3 of Eiroku 12 (1569) requested reinforcements from Kobayakawa Takakage who was based in Chōfu in Nagato Province.  On 10/25, after having defeated Ōuchi Teruhiro, Mōri Terumoto immediately returned to Aki Province and, on 1/6 of Eiroku 13 (1570), deployed to Izumo with Terumoto as the commanding general of the Mōri forces.  Motoaki followed Terumoto to support the defenders at Gassantoda Castle while the Mōri army launched a counterattack that resulted in the defeat of the Amago revival army.  By this means, Motoaki was ordered to serve as the commander-in-charge of Gassantoda Castle.  Owing to this appointment, his adoption by the Suginomori family was dissolved and he reverted to the name of Mōri Motoaki or, based on the place name, Toda Motoaki.

In the second month of 1578, Bessho Nagaharu of Harima Province surrendered to the Mōri so Kikkawa Motoharu and Kobayakawa Takakage served in the vanguard of forces deploying to Harima.  Motoaki affiliated with the army of Motoharu and participated in the Siege of Kōzuki Castle.

On 5/5 of Tenshō 13 (1585), Motoaki died of illness at Gassantoda Castle at the age of thirty-four.  His grave is on the remains of the Sōshō Temple near the castle.  After his death, before long, his son also died so his landholdings were inherited by his younger brother of the same mother, Suetsugu Motoyasu.

Motoaki had an illegitimate son named Senmanmaru.  In the genealogy of the Ninagawa family, there is a reference to Senmanmaru in the exploits of a retainer of Motoaki named Ninagawa Akihide.  After the death of Motoaki in 1585, Akihide informed Mōri Terumoto in regard to the existence of Senmanmaru as an illegitimate son of Motoaki and, together with Akagawa Yukitake, planned to serve as retainers of Senmanmaru, but Senmanmaru died from smallpox at the age of three.

Motoaki also had a daughter.  In a compilation of genealogical charts of families from Bōchō, there is a reference to her in the chart of the Asa-Mōri family, but she was frail of health, so did not marry and was raised by a cousin named Mōri Motonobu.  She has a posthumous Buddhist name​ but the identity of her mother and real name are unknown.  She died on 12/4 of Manji 2 (1659) and was buried in the same location as Motonobu on Mount Hōshu in the Asa District of Nagato Province.

In this genealogical chart, there is no reference to Motoaki’s wife (the daughter of Mizawa Tamekiyo) or his illegitimate son, Senmanmaru.