Phitchaya Sunthonthuam gained his first international experience at the Junior Asian Championships 2016 in Ho Chi Minh City , where he won the gold medal in the 4 x 400 meter relay in 3: 11.59 minutes. He qualified for the U20 World Championships in Bydgoszcz , where he was eliminated in 3: 10.08 minutes in the lead. At the 2017 Asian Championships in Bhubaneswar , India , he won the bronze medal behind the teams from India and Sri Lanka in 3: 06.48 min. At the Southeast Asian Games in Kuala Lumpur he won gold with the relay and in 46.46 s silver in the individual competition behind the Filipino Trenten Beram . At the beginning of September he won the bronze medal behind Pakistan and Qatar at the Asian Indoor & Martial Arts Games in Ashgabat with the relay in 3: 21.21 minutes and reached the semifinals over 400 meters, in which he was eliminated with 51.22 seconds. In 2018 he finished fourth in the Junior Asian Championships in Gifu in 47.26 seconds and won the silver medal behind Sri Lanka in 3: 09.20 minutes in the relay. At the end of August he took part in the Asian Games in Jakarta for the first time , where he retired with the men's relay in the lead, while he finished sixth with the mixed relay in 3: 25.80 minutes.
In 2019 he reached the semi-finals at the Asian Championships in Doha , where he was eliminated with 47.15 s. In addition, he came fourth with the relay in 3: 10.28 min. He then made it to the semifinals at the Summer Universiade in Naples , where he was eliminated with 47.38 seconds, while he was sixth in the relay in 3: 06.00 minutes. At the beginning of December he won the bronze medal behind the Vietnamese Hoàng Trần Nhật and Trần Đình Sơn at the Southeast Asian Games in Capas in 46.98 s . He also secured the silver medal behind Vietnam with the relay in 3: 08.20 minutes.
Personal best
400 meters: 46.46 s, August 24, 2017 in Kuala Lumpur
400 meters (hall): 48.96 s, September 18, 2017 in Ashgabat
Thailand
