The unity government of the Sri Lanka Freedom Party (SLFP) and the United National Party (UNP) was thrown into a crisis after former president Mahinda Rajapaksa's new party pulled off a stunning victory in local elections seen as a referendum on the ruling alliance.
Former strongman Rajapaksa's nearly a decade-long rule was ended by Sirisena in 2015.
Several portfolios have been reshuffled among the UNP members with some of them exchanging jobs.
"Taking (into account) people's message expressed at the recent local government election, the government needs to improve its policies, programmes and actions to serve people," Sirisena said in a tweet.
Handing out the new appointments Sirisena expressed hope that the changes will serve the people better.
Rajapaksa's new political party, Sri Lanka People's Party (SLPP), defeated Sirisena's SLFP and Wickremesinghe's UNP, winning 225 councils or two thirds of the 340 councils which went to polls earlier this month.
After registering the landslide win, Rajapaksa was quick to demand a snap general election which is scheduled to be held after August 2020.
Since the defeat, Sirisena has been seeking the removal of Wickremesinghe as the prime minister, attempting to form his own SLFP government, analysts have said.
However, in the absence of required numbers, Sirisena has to accept Wickremesinghe, they said.
Wickremesinghe has said that the result of the local body polls was a wake up call for the government.