Baruah, who took oath in Assamese, was recently elected from Lakhimpur Lok Sabha constituency which was vacated by Assam Chief Minister Sarbananda Sonowal when he was elected to the State Assembly earlier this year.
Baruah was a four-time MLA and had joined the BJP from Congress late last year.
He defeated his nearest Congress rival Hema Hariprasanna Pegu by a margin of over 1,90,000 votes in the bye-elections held this month.
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