| Julien Watrin | |
| Birth Date: | 27 June 1992 |
| Birth Place: | Virton, Belgium |
| Height: | 1.87 m |
| Weight: | 82 kg |
| Country: | Belgium |
| Sport: | Athletics |
| Event: | 400 metres, 400 m hurdles |
| Club: | AC Dampicourt |
| Coach: | Edith Graff |
Julien Watrin (born 27 June 1992) is a Belgian sprinter specialising in the 400 metres. In 2023, he won his first individual major senior medal, with silver at the European Indoor Championships. Watrin earned several major medals with national men's 4 × 400 m relays, including bronzes at the 2019 and 2022 World Athletics Championships.
He is the Belgian record holder for the 400 m hurdles, Belgian indoor record holder for the 400 m, and won several national titles.
| 2009 | European Youth Olympic Festival | Tampere, Finland | bgcolor=silver | 2nd | 100 m | 10.82 |
| bgcolor=gold | 1st | 200 m | 21.06 | |||
| 3rd | 4 × 100 m relay | 41.69 | ||||
| 2010 | World Junior Championships | Moncton, Canada | 7th | 100 m | 10.56 | |
| 9th (sf) | 200 m | |||||
| 13th (h) | 4 × 100 m relay | 40.43 | ||||
| 2011 | European Junior Championships | Tallinn, Estonia | – | 200 m | DNF | |
| 2013 | European U23 Championships | Tampere, Finland | bgcolor=gold | 1st | 4 × 400 m relay | 3:04.90 |
| Jeux de la Francophonie | Nice, France | 4th | 200 m | 21.56 | ||
| 3rd | 4 × 100 m relay | 39.58 | ||||
| 2014 | World Relays | Nassau, Bahamas | 1st (B) | 4 × 400 m relay | 3:02.97 | |
| European Championships | Zürich, Switzerland | 23rd (h) | 400 m | 46.31 | ||
| 7th | 4 × 400 m relay | 3:02.60 | ||||
| 2015 | European Indoor Championships | Prague, Czech Republic | bgcolor=gold | 1st | 4 × 400 m relay | 3:02.87 |
| World Relays | Nassau, Bahamas | 3rd | 4 × 400 m relay | 2:59.33 | ||
| 2016 | European Championships | Amsterdam, Netherlands | 10th (sf) | 400 m | 45.76 | |
| bgcolor=gold | 1st | 4 × 400 m relay | 3:01.10 | |||
| Olympic Games | Rio de Janeiro, Brazil | 4th | 4 × 400 m relay | 2:58.52 | ||
| 2017 | European Indoor Championships | Belgrade, Serbia | bgcolor=silver | 2nd | 4 × 400 m relay | 3:07.80 |
| World Relays | Nassau, Bahamas | 2nd (B) | 4 × 400 m relay | 3:07.14 | ||
| 2018 | European Championships | Berlin, Germany | 4th (h) | 4 × 400 m relay | 3:02.55 | |
| 2019 | European Indoor Championships | Glasgow, United Kingdom | 1st | 4 × 400 m relay | 3:06.27 | |
| World Relays | Yokohama, Japan | 8th (h) | 4 × 400 m relay | 3:03.70 | ||
| World Championships | Doha, Qatar | 3rd (h) | 4 × 400 m relay | 3:00.87 | ||
| 2022 | World Indoor Championships | Belgrade, Serbia | 6th (sf) | 400 m | 46.54 | |
| bgcolor=gold | 1st | 4 × 400 m relay | 3:06.52 | |||
| World Championships | Eugene, OR, United States | 14th (sf) | 400 m hurdles | 49.52 | ||
| 3rd | 4 × 400 m relay | 2:58.72 | ||||
| European Championships | Munich, Germany | 6th | 400 m hurdles | 48.98 | ||
| bgcolor=silver | 2nd | 4 × 400 m relay | 2:59.49 | |||
| 2023 | European Indoor Championships | Istanbul, Turkey | bgcolor=silver | 2nd | 400 m | 45.44 |
| bgcolor=gold | 1st | 4 × 400 m relay | 3:05.83 | |||
| World Championships | Budapest, Hungary | 17th (sf) | 400 m hurdles | 48.94 | ||
| 9th (h) | 4 × 400 m relay | 3:00.33 |