[2] Kawauchi is a frequent competitor, entering many races each year (averaging a marathon per month) ranging in distance from the 1500 m to the 50 km ultramarathon.

[4] Born in Setagaya, Tokyo,[5] Kawauchi began running from a young age: first he practiced with his mother and later with the track teams at high school.

[6] He began to break into the upper echelons of the national scene at the 2010 Tokyo Marathon, where he claimed fourth place in a personal-best time of 2:12:36.

[9] He set his sights on a top-eight finish at the Tokyo Marathon later that month but exceeded his own expectations by running a time of 2:08:37 and taking third place.

[10] In June, he entered the Okinoshima Ultramarathon and led the 50 km race right up to the last 600 metres, at which point he collapsed due to heat stroke.

The Japan Association of Athletics Federations played down his selection choices, saying that his time of 2:09:57 was not fast enough, but Kawauchi upturned tradition by saying the race was a warm-up for the second qualifier in Tokyo.

[14] At the start of 2012, Kawauchi ran a half-marathon best of 1:02:18 in Marugame, but his unorthodox decision to race frequently ruined his chances of Olympic selection, as he finished fourteenth with a time of 2:12:51 at February's Tokyo Marathon.

"[19] The organizers of the 2013 Egyptian Marathon agreed to pay his travel expenses for the January race, but Kawauchi missed his flight after arriving at the airport without his passport.

[21] Less than three weeks later he ran at the Beppu-Ōita Marathon and reached the top of the Japanese rankings by winning the race in a personal best of 2:08:15, breaking Gert Thys's 17-year-old course record in the process.

[22] He beat a number of professional runners at the Kumanichi 30 km Road Race two weeks later, finishing in 1:29:31—another course record and a personal-best time.

After leading early at world record pace and repeatedly surging throughout the race, at mile 25 Kawauchi passed defending champion Geoffrey Kirui to achieve his first major marathon win.

[30] After returning to Japan following his Boston Marathon win, Kawauchi told reporters that he would quit his job as a high school administration office worker and turn pro in April 2019.

[31] Kawauchi married fellow runner Yuko Mizuguchi [ja] in May 2019, about two weeks after they both won their gender class in the Vancouver Marathon.