Speaker Karu Jayasuriya allowed Prime Minister Ranil Wickremesinghe to move motion in Parliament to increase the number of Cabinet Ministers.
Announcing his verdict, Jayasuriya said that there was no need for all parties to join in forming a national government.
Several MPs had argued that a national government has not been formed since there was an opposition in the Parliament.
The UNP and the SLFP recently signed a MoU on forming a national government. However, a section of the UPFA MPs opposed this. Both the TNA and the JVP also remain in opposition.