Having begun playing cricket as a top-order batsman, Prasad became a fast bowler in his late teens and played in the 2002 Under-19 World Cup.

In February 2006, he was called up to Sri Lanka's ODI and Test squads for a tour of Bangladesh after bowling at an average of less than 23 runs per wicket in domestic first class cricket. He made his ODI debut on the tour, taking 2/29 in a 78-run win over Bangladesh in Chittagong.

Prasad's international career was subsequently affected by a back injury. He had to wait until August 2008 to make his Test debut, taking five wickets over both innings of the third Test of India's tour of Sri Lanka, including those of Sachin Tendulkar, who Prasad said was his favourite player, Rahul Dravid, and Virender Sehwag. He played Test cricket sporadically over the following seasons. He took four wickets in the first Test of Sri Lanka's tour of Bangladesh in December 2008, but was dropped for the second Test.

In 2009, he played in the second Test of Sri Lanka's home series against New Zealand and the first Test of Sri Lanka's tour of India, in which he injured his hamstring. In 2010, Prasad played in one Test against India and another against the West Indies, failing to take any wickets on either occasion.

In June 2011, Prasad was recalled to Sri Lanka's ODI squad for the tour of England and Scotland. He played in two ODIs on the tour, taking two wickets against England and three against Scotland.^[14] He was named in the Test squad for Australia's tour of Sri Lanka in August and September, but did not play. He did, however, make his international Twenty20 debut against Australia,^[15][16] before playing in two Tests of Sri Lanka's series against Pakistan in the United Arab Emirates.^[12] He was called into Sri Lanka's squad for their tour of South Africa in 2011–12 as a replacement for injured bowlers. He played in the third and deciding Test of the series, which Sri Lanka lost, taking two wickets for 156 runs, and also played in two ODIs.^[17]