He is the seventh Speaker of the National Assembly of Kenya, in office since 2013. He is the first Speaker to serve following the reestablishment of a bicameral Parliament, as mandated by the 2010 Constitution. On 28 March 2013, Muturi won the speakership after a second round of voting by Members of the National Assembly, beating former speaker Kenneth Marende by a 219–129 margin.

Muturi was first elected as a member of the Kenya African National Union to represent Siakago Constituency in Parliament following a 1999 byelection. He won reelection in 2002 and served as opposition chief whip and chair of the Public Investment Committee during the 10th Parliament. He vied for re-election in 2007, but was defeated by Lenny Kivuti.

In 2013, Muturi ran for the Mbeere North parliamentary seat as a member of The National Alliance party, but lost to Muriuki Njagagua.

He served as a member of the Parliamentary Select Committee on the constitutional review from 1999 to 2004. He was elected KANU National Organising Secretary in Nov 2008 and was the PNU constitution committee chairman during the national constitutional talks from 2008–2010. In April 2011, he was appointed the chairman of the Centre for Multiparty Democracy (CMD), a civil society group that deals with democracy issues in multi-party politics.

Muturi was formerly a judiciary employee serving as a principal magistrate between 1982 and 1997 before retiring from judicial service. He also served as the chairman of the Judges and Magistrates Association during the time. He was a member of the Africa Parliamentarians Network Against Corruption, Global Organisation of Parliamentarians Against Corruption and the Parliamentary Network on the World Bank.