Susanthika won the third place in the 200m event at the 2000 Sydney Olympic Games with a time of 22.28s, becoming the second Sri Lankan to win an Olympic Medal after Duncan White.
Her performance was later upgraded to a Silver Medal after the winner of the 200m event Marian Jones was stripped following a doping test. Her Silver Medal achievement at the 2000 Sydney Olympics also stood as the only Olympic Medal for a South Asian in athletics for 21 years.
Susanthika had the honour of representing the country at four Olympic Games in 1996, 2000, 2004 and 2008.
After retiring from the sport, she joined the Sports Ministry as the Director of Talent Search and Olympic Director High-Performance.