Suzuki Sadayū was a kokujin, or provincial landowner, in Kii Province during the Sengoku period. Sadayū was a member of the Saikatō-Suzuki clan. He is surmised to be the father of Suzuki Magoichi who is known for his exploits fighting on behalf of the Ishiyama-Hongan Temple during the Ishiyama War against Oda Nobunaga that persisted from 1570 to 1580.
References to Sadayū appears in chronicles of the Kishū domain compiled in the latter Edo period and other records from Kii Province. According to these accounts, Sadayū served as the lord of Saika Castle in the Nagusa District of Kii and governed a fief of 70,000 koku.
In 1585, during the Conquest of Kishū by Hashiba Hideyoshi, Sadayū’s son, Magoichi, joined others in the resistance. Details regarding Sadayū’s movements during this period are unknown, but, after the surrender of the Saika Group, he is said to have committed seppuku in the town of Kokawa after being deceived by Tōdō Takatora, a bushō on the side of the Hashiba. Another account notes that Saika Castle was toppled by Oda Nobunaga, so there are inconsistencies regarding the timing of his demise.