The main stock index ended up 0.5 percent, or 35.69 points, at 7,198.44, its highest close since Jan.30.
Analysts, however, said political uncertainty weighed on the bourse, with the Opposition bringing in a no-confidence motion against a cabinet minister and the Prime Minister threatening to dissolve parliament if it goes through.
"Bit of a slow day. The turnover was comparatively low. This slowdown might there for some days until they settle at the parliament," said Dimantha Mathew, manager, research at First Capital Equities (pvt) Ltd.
Monday's turnover was 930 million rupees ($7 million), well below this year's daily average of 1.43 billion rupees.
Shares of Hatton National Bank Plc rose 5.59 percent, while conglomerate John Keells Holdings Plc gained 1.44 percent.
Foreign investors bought a net 92.2 million rupees worth of shares on Monday, extending net foreign inflows this year to 825.4 million rupees worth of shares. The bourse had net foreign inflows of 22.07 billion rupees last year.
($1 = 132.8000 Sri Lankan rupees) (Reporting by Ranga Sirilal and Shihar Aneez; Editing by Prateek Chatterjee)