The main stock index rose 0.16 percent, or 11.40 points, to 7,326.31, its highest close since Feb. 13.
Shares in Ceylon Tobacco Co Plc rose 2.32 percent.
Turnover was 1.01 billion rupees ($7.6 million), well below this year's daily average of 1.43 billion rupees.
"Investors still don't have 100 percent confidence because of political uncertainty and buying is very low despite billion-rupee turnover today."
Parliamentary election is expected after April 23 and there is still uncertainty around whether new President Maithripala Sirisena's coalition would contest together or separately.
Foreign investors were net buyers of 98.3 million rupees worth of shares on Monday, ending three straight sessions of net outflows and extending the year-to-date net foreign inflows to 1.36 billion rupees.
The bourse saw net foreign inflows of 22.07 billion rupees in 2014. ($1 = 132.9000 Sri Lankan rupees) (Reporting by Ranga Sirilal and Shihar Aneez; Editing by Prateek Chatterjee)