He studied at Mahanama College, Colombo 03.
He is a left-handed batsman and right-arm medium-fast bowler who plays for Colombo. Gunathilleke made his cricketing debut in the 2007-2008 Inter-Provincial Twenty20 tournament for Sri Lanka Schools, alongside fellow Colts Cricket Club player Kusal Perera. Gunathilleke made his List A debut for Colombo Cricket Club against Sinhalese Sports Club in 2009-2010, scoring a single run.
He made his One Day International debut for Sri Lanka against the West Indies on 1 November 2015.
After Kusal Perera dropped from the 2015-2016 New Zealand tour due to drug scandal, Gunathilaka was included to the ODI squad for opening position with Tillakaratne Dilshan. His batting ability did not showed in the first two ODIs, but in the third ODI which was his only 4th international match, Gunathilake scored a fast and dashing 65 runs from 45 balls.
The innings included 7 fours and 4 sixes and getting the match away from New Zealand. During the same tour, he made his Twenty20 International debut for Sri Lanka against New Zealand on 7 January 2016.
One Day Internationals - Manitoba of the Match awards.
