Sidhu, who was speculated to become the Deputy Chief Minister, was given the "No. 3" slot.
During the swearing-in ceremony here earlier in the day, Sidhu was administered the oath of office and secrecy by Punjab Governor V.P. Singh Badnore after Amarinder Singh and cabinet minister Brahm Mohindra.
Sidhu, who joined the Congress in January ahead of the February 4 assembly elections, won the Amritsar-East assembly seat by over 42,000 votes.
He was earlier an MP from Amritsar when he was part of the Bharatiya Janata Party (BJP). He was elected to the Lok Sabha in 2004, 2007 (by-election) and 2009.
He was nominated to the Rajya Sabha by Prime Minister Narendra Modi government in April 2016.
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