In March, Watanabe won both the men's and mixed doubles disciplines in the All England Open with Hiroyuki Endo and Arisa Higashino. They are the first players in over 19 years to accomplish such a feat. In July, he competed at the 2020 Tokyo Olympics in the men's doubles partnering Endo, and in the mixed doubles with Higashino. Watanabe and Endo pace was stopped in the quarter-finals to Lee Yang and Wang Chi-lin, while in the mixed doubles, Watanabe and Higashino clinched a bronze medal after winning the match against Tang Chun Man and Tse Ying Suet in straight games.