"The president signed a gazette notification dissolving parliament with effect from midnight on Friday," BBC quoted government spokesman Rajitha Senaratne as saying.
The general elections were not scheduled for another 10 months.
Sirisena defeated incumbent Mahinda Rajapaksa in presidential elections held in January.
Sirisena's decision to dissolve parliament came shortly after a spokesman for the United National Party (UNP) said it had formally requested him to do so.
The UNP was the main party behind Sirisena's presidential bid and its leader, Ranil Wickremesingha, is the country's prime minister.