The decision to appoint Raja to the post of general secretary was taken at the party's national council meeting which began on Friday.
The CPI which is the second largest party of the left front has been facing its worst crisis ever with its electoral numbers at an all-time low. The party managed to secure just two seats in the recently concluded Lok Sabha elections. Both the candidates won from Tamil Nadu.
"The country is going through a critical period under the fascist regime of (Prime Minister) Narendra Modi. The Left might have lost seats in the Lok Sabha election and might have been reduced to a smaller force in Parliament, but it does not mean that we have shrunk within the country or our ideological and political influence has shrunk," Raja said at a press conference.
He said he wants all communist parties to come together and rework their strategies.
Seventy years old Raja is a two-time Rajya Sabha member from Tamil Nadu. His term at the Upper House comes to end on 24 July.