- "I will lose nothing if I lose power," he said in an emotional speech
- He headed straight to the Governor's house to resign from the assembly
- BJP, with 103 seats, was eight short of the majority-mark - 111
Here's your 10-point cheatsheet to this big story:
"I come from a background of struggle. I will lose nothing if I lose power... I am going straight to Governor's house to give my resignation," Mr Yeddyurappa told the assembly, just a little over 48 hours after he was sworn-in as chief minister.
It was Mr Yeddyurappa's third stint as chief minister, also his shortest. The BJP leader had quit in a week in 2007, again before the assembly was to vote on his confidence motion.
Turning to the Congress-JDS combine chief ministerial candidate HD Kumaraswamy, Mr Yeddyurappa said, "Dear Kumaraswamy, I am a fighter and I will fight till my last breath".
Soon after an emotionally charged 20-minute speech, Mr Yeddyurappa walked out of the assembly while the national anthem was being played. He headed straight to the Raj Bhavan to submit his resignation. BS Yeddyurappa's party, the BJP, with 104 seats, was eight short of the majority-mark - 111.
Karnataka has rejected the BJP's arrogance, Congress president Rahul Gandhi told reporters in his victory speech after Mr Yeddyurappa's resignation. He added that the Karnataka outcome means that the opposition will unite to defeat the BJP.
The trust vote was ordered by the Supreme Court on a petition by the Congress and JDS challenging governor Vajubhai Vala's decision inviting Mr Yeddyurappa to form the government and prove his majority in 15 days after election results were announced on Tuesday.
The Congress challenged his decision in the Supreme Court the same night. After an all-night hearing, the court didn't stop Mr Yeddyurappa's oath ceremony, but said it would continue hearing the case. Resuming the hearing yesterday, the Supreme Court ordered Mr Yeddyurappa to take a strength test today.
Mr Yeddyurappa's resignation would pave way for the Congress-JDS combine to form the government in Karnataka. The two parties were quick to form an alliance with JDS chief HD Kumaraswamy as their head after the Karnataka results put them in second and third position. Together they have 117 members, enough for an outright majority.
The opposition Congress and Janata Dal accused the BJP of trying to bribe and threaten their lawmakers. Earlier today, the Congress released audio tapes as proof. The tapes have BJP leaders including Mr Yeddyurappa allegedly trying to persuade Congress lawmaker BC Patil to switch sides.
In a dramatic turn of events, two Congress lawmakers Pratap Gowda Patil and Anand Singh, who had been 'missing' for days, reached the Karnataka assembly just before the trust vote and took oath as the members. The Congress and JDS lawmakers were constantly on the move as their parties tried to sequester them from attempts to bribe, threaten or induce them into switching over to the BJP. They were brought in this morning from Hyderabad in buses after an overnight journey.