Prime Minister Narendra Modi’s right-wing Bharatiya Janata Party (BJP) failed to secure enough votes to make a clear win in the May 12 elections, as with centre-left opposition groups Congress and Janata Dal (Secular).
The Karnataka elections are the first test of power for Mr Modi’s party in 2018 ahead of general elections in India next year.
Home to 66 million people, the state is also the technology hub of Benglauru.
Karnataka is India’s first region out of four to elect an assembly this year, with Mr Modi keen to hold onto seats in the face of criticism about a introduced nationwide sales tax and ban on high-value bank notes in 2016.
BJP vs JD – who won? Has government been sworn in?
The election resulted in a hung parliament despite BJP emerging as the single largest party, taking 104 seats in the 225-member assembly.
But in dramatic fashion, the result was challenged by main opposition Congress party, which said it had a combined vote count of 117 as part of a coalition with JD(S).
Despite this, BJP’s B S Yeddyurappa was sworn in as Chief Minister of Karnataka at 9am local time today (4.30am BST).
The leader took his oath after being invited to form a government a day earlier by governor Valubhai Vala, who said BJP needed to prove its majority within 15 days.
His action was challenged by the opposition alliance in the Supreme Court on Wednesday night.
Senior lawyer Ram Jethmalani said the government’s decision was a “gross abuse of constitutional power”.
But the court refused to stay the swearing-in, although it stated the final government formation would depend on the 15-day verdict.
At his first press conference since the swearing-in today, Mr Yeddyurappa rejected the Congress-JD(S) coalition as “unholy” and said the people had “rejected them outright”.
He said: “I am sure of winning the vote of confidence and my government completing five years.”
If BJP is successful that will mean the party will govern 22 out of 29 states in the country.
Who is B S Yeddyurappa?
Mr Yeddyurappa has been a politician since 1970 when he was appointed as Secretary of the right-wing and paramilitary volunteer organisation Rashtriya Swayamsevak Sangh (RSS)’s Shikaripur unit.
RSS is seen as the parent group of BJP and is the world’s largest voluntary missionary organisation.
He first took office as chief minister in 2008 but resigned in 2011 after iron ore illegal export scam.
After returning to the part in 2013, he successfully won the Shimoga seat (Karnataka) in the national 2014 election.
He was re-appointed as President of Karnataka in 2016.