Watanabe was born in the Urakawahara suburb of Joetsu, Niigata Prefecture, Japan on 5 March 1907. He was the first of eight children born to Haruzo and Miya Watanabe, who were farmers. After graduating from an agricultural high school, Watanabe worked for Dai-Nippon Meiji Sugar and moved to Taiwan to help conclude sugar cane plantation contracts there.
During his 18 years in Taiwan, Watanabe married his wife, Mitsue, and four out of their five children were born there. He also served in the military towards the end of the Pacific War in 1944. He returned to Niigata after the war and worked for a departure agency.
In 1974, Watanabe and his son Tetsuo built a new family home, which had about a hectare worth of farm next to it. He also worked on his bonsai until he was set to live in a nursing home. He also presented his work at local exhibitions until 2007.
After retiring, Watanabe lived with one of his son’s family until the age of 108, when he moved to a care facility in Joetsu, Niigata, Japan. As of 2019, he had 12 grandchildren and 16 great-grandchildren. In January 2019, in an interview for a local newspapers, he said that the secret to his longevity was to “not to get angry and keep a smile on your face”.
Watanabe died in his hometown on 23 February 2020, at the age of 112 years, 355 days, eleven days before his 113th birthday.