BBC: He said Turkey’s secular and democratic character was “not up for debate”.
His comments came a day after a key member of the ruling AK party (AKP) called for secularism to be taken out of the constitution.
Parliamentary speaker Ismail Kahraman, who is overseeing the draft charter, said Turkey was a Muslim country and should have a religious constitution.
Turkey is a Nato member and aspires to join the EU, which has traditionally regarded the country as a model of secular democracy in the Islamic world.
But critics of the government fear the modern state’s secular foundations are being eroded.
Opposition parties also fear the new constitution could concentrate too much power in the hands of President Recep Tayyip Erdogan, who wants an executive presidency to replace the current parliamentary system.
In a speech on Wednesday, Mr Davutoglu said: “Secularism will feature in the new constitution we draft as a principle that guarantees citizens’ freedom of religion and faith and that ensures the state is an equal distance from all faith groups.”