He has contested to Kerala Legislative Assembly from Chengannur constituency in 2006 and lost to P. C. Vishnunath of Indian National Congress by a margin of 5321 votes. He was elected to Kerala Legislative Assembly from Chengannur constituency in the by-election held on 28 May 2018 necessitated by the demise of K. K. Ramachandran Nair. He won with a margin of 20956 votes defeating Adv. D. Vijayakumar of Indian National Congress. Saji Cheriyan has recorded the best winning-margin for an LDF candidate in an Assembly election in Chengannur.

On 17 August 2018, his controversial Facebook post went viral among social media, stating his helplessness and request to the central government, regarding his constituency, which was at a highly dangerous zone during 2018 Kerala floods. Aftermath, actions were taken in order to save Chengannur.

Cheriyan’s entry into politics was through Students’ Federation of India, the student cadre of CPI(M), of which he was once the Alappuzha district secretary and later the president. He rose through the ranks and went on to become the district president of Democratic Youth Federation of India, the youth wing of CPI(M). He represented Mulakuzha division in the district panchayat in 1995 and became chairman of the development standing committee in the local body. He was elected CPM Chengannur area secretary in 2001. He has also holds positions of Area Committee Secretary of CPI(M), Member of Alappuzha Jilla Panchayath, Kerala University Syndicate member, and CITU district President.

Saji Cheriyan was born on May 28, 1965 at Kozhuvalloor, Alappuzha district. He has a Bachelor of Arts degree from Bishop Moore College, Mavelikara. Saji Cheriyan is married to Christina Cherian and they have three daughters.