An announcement in party mouthpiece Saamna said the decision had been taken at a meeting of top party leaders at the Thackeray residence Matoshri.
"All the powers of Shiv Sena Pramukh (chief) shall be with executive president Uddhav Thackeray. This has been decided in a meeting of Shiv Sena leaders," the statement said, in a development that was anticipated.
Uddhav, 52, has been the party's executive president since 2004. He will now be de facto party president. His father Bal Thackeray had founded the party and led it for over four decades till his death Nov 17.
After Bal Thackeray's demise, a photograph with a sandalwood garland has been placed on the chair he regularly used.
"The party's first meeting was held in 'Thackeray Durbar' (the room where the garlanded photograph of the late Shiv Sena chief has been placed) where all the leaders unanimously expressed confidence in Uddhav and decided to authorise him (Uddhav Thackeray) to fulfil the late Bal Thackeray's dreams," the statement said.
Thackeray was accorded a public, state funeral Nov 18 at Shivaji Park, with nearly two million people taking part in the funeral procession.