He was earlier the Chief Financial Officer.
"In his new role, Ranjan would be responsible for mergers and acquisition, internal audit, internal control as well as the admin function while continuing work on improving group level governance," the company said in a statement.
Viacom 18 has also promoted Soumen Ray as the Chief Financial Officer of the company. Ray was earlier the deputy CFO.
Both the managerial changes will be effective tomorrow.
"With a 30X growth in topline since inception, we are one of India's fastest growing M&E companies. As we gear up for a more streamlined growth phase, it is imperative to align our corporate functions so that we can leverage both the experience and the expertise that our leaders possess," Viacom18 Group Chief Executive Officer Sudhanshu Vats said.
"Ray, who as the Deputy CFO, has been pivotal in streamlining the network's financial performance, will now take over as the CFO," he added.