Foreign investors bought a net 1.2 billion rupees ($7.71 million) worth of shares, extending the year-to-date net foreign inflow to 7.3 billion rupees worth of equities.
Analysts said local and foreign investors returned to the market a week after a wave of anti-Muslim attacks by Sinhalese Buddhist hardliners in the central highlands district of Kandy.
The Colombo stock index ended 0.11 percent firmer at 6,554.83.
"It is a positive sign that both locals and foreigners are buying after a long wait," said Dimantha Mathew, head of research, First Capital Holdings.
Turnover was 2.5 billion rupees on Tuesday, the highest since Feb. 26 and more than double of this year's daily average of around 960.4 million rupees.
Shares in Asian Hotels and Properties Plc ended up 3.8 percent, Dialog Axiata Plc gained 1.5 percent and Singer Sri Lanka Plc rose 2.7 percent.