He was administered the oath of office by Gauhati High Court Chief Justice Ajit Singh at a function in the Srimanta Sankardeva International Convention Centre here.
Chief Minister Sarbananda Sonowal, his cabinet colleagues and senior officials were present at the swearing-in ceremony.
In his previous assignment, Mukhi served as the Lieutenant Governor of Andaman and Nicobar Islands.
He succeeded Banwarilal Purohit who has been appointed as the Governor of Tamil Nadu.
Mukhi offered prayers at Kamakhya Temple after assuming charge.
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The governor told reporters outside the temple that he feels blessed and is grateful to President Ram Nath Kovind for appointing him as the governor of Assam.
As governor, "I will work with my government and ensure that welfare of people are taken care of and decisions are taken according to rules and law of the land", he said.
The governor also visited Bhupen Hazarika's Memorial at Jalukbari and planted a sapling there.