Aruna Dharshana gained his first international experience at the Junior Asian Championships in Ho Chi Minh City , where he finished fifth in the Sri Lankan 4 x 400 meter relay in 3: 12.77 minutes. Two years later he took part again in the Junior Asian Championships in Gifu and won there with a new championship record of 45.79 s over 400 meters. He also won the season in 3: 08.70 min. He qualified for the U20 World Championships in Tampere , Finland , where he reached the semifinals over 400 meters and reached eighth place in the relay in the final. At the end of August he took part in the Asian Games in Jakarta for the first time and reached the semi-finals in the individual competition and was fourth in the relay in 3: 02.74 min. The following year, he finished at the Military World Games in Wuhan in 48.07 s eighth and prevailed then in 46.69 seconds at the South Asian Games in Kathmandu in the individual event as well as in 3: 08.04 min with the season.
In 2018 and 2019 Dharshana became Sri Lankan champion in the 400-meter run.