Mendis made his debut for Sri Lanka in 1972, batting at number three against the visiting Tamil Nadu side. Mendis top-scored in the first innings with 52, and also made 34 in the second innings, but could not prevent an innings defeat. This match did not have international status, and indeed Mendis represented Sri Lanka in a number of non-internationals. His first ODI, however, came in 1975, when he made 8 against the West Indies in a batting collapse. It took seven more years before Mendis got to play a Test match; on 17 February 1982 he joined forces with the other Sri Lankans against England. In that match, he was sent in to bat at number four, but only made 17 and 27 in Sri Lanka's seven-wicket defeat. More defeats followed, and in his first eight innings he only recorded one fifty, in the first Test of three against Pakistan.