The swearing-in ceremony took place in Shimla, where MP Rahul Gandhi and the party's general secretary Priyanka Gandhi Vadra were also present.
Further, Mukesh Agnihotri, who served as the leader of Opposition in the outgoing Assembly, was administered the oath as the deputy CM.
Chhattisgarh Chief Minister Bhupesh Baghel had announced the Congress party's decision on Saturday.
After the announcement was made, Sukhu said:
"It is my responsibility to fulfil the promises we made to the people of Himachal Pradesh. We have to work for the development of the state."
Thanking Rahul, Priyanka, and Sonia Gandhi, he said that his deputy, Agnihotri, and he will work as a team.
Who Is Sukhvinder Singh Sukhu?
Sukhu, 58, is a four-time MLA from Nadaun in the state's Hamirpur district. He fought his first state election in 2003 and has won all the polls he fought since then, barring the one in 2012.
A lawyer by profession, the leader rose through the ranks of the National Student Union of India (NSUI) – the student body of the Congress.
He even led the NSUI's state unit from 1985-1988 and was an activist while he was studying at Himachal Pradesh University.
Later, Sukhu served as the state president of the Youth Congress for a period of 10 years, from 1988 to 2008.
Having won municipal polls from Shimla twice, he was made secretary of the state unit in 2008.
He has held the post of the party's campaign committee as well and is a former president of the Himachal Pradesh Congress Committee.
Sukhu is a strong Thakur face of the party and has been a counterweight to the Dhumal family in Hamirpur. In the 2022 state election, he defeated the BJP's Vijay Kumar by 3,300 votes to be elected from the Nadaun constituency.
The decision to appoint Sukhu as the next CM came a day after a meeting of newly elected Congress MLAs, at the party office in Shimla, to choose the next chief minister. At the meeting, the MLAs unanimously passed a resolution authorising the party president to pick the next CM.
The Congress won the elections in the hill state on Thursday, with 40 seats in the 68-member Legislative Assembly. Sukhu was among the three names being floated for the next CM – the other two being Pratibha Singh and Mukesh Agnihotri.
On Friday, supporters of Singh and Sukhu were seen coming face-to-face outside the party office, raising slogans in support of their respective leaders, in a show of strength.
However, after the announcement to appoint Sukhu to the top post was made, Singh said that she "accepts" the decision taken by the Congress high command.
(With inputs from ANI and PTI.)