"I hereby tender my resignation as the Chief Minister of Karnataka along with my cabinet and request you to accept the same," Kumaraswamy said in the letter submitted to Governor Vajubhai Vala at the Raj Bhavan.
Accepting the resignation, the Governor asked Kumaraswamy to continue as the caretaker Chief Minister till alternative arrangements were made.
"It is needless to state that no executive decisions be taken during the period," said the Governor in his letter to Kumaraswamy, added the communique.
The Bharatiya Janata Party (BJP) will stake claim to form the next government in Karnataka on Wednesday after meeting the Governor, state BJP leader R. Ashoka said.
Kumaraswamy lost the floor test by 6 votes after a four-day marathon debate on the motion that witnessed heated exchanges and acrimonious scenes in the House.
"Chief Minister Kumaraswamy has lost the floor test, as 99 votes were in favour of the confidence motion and 105 against it," Assembly Speaker K.R. Ramesh Kumar told the members of the House after the trust vote.
Of the 225-member Assembly, 20 legislators were absent for the floor test, reducing the House strength to 205 with 103 as the halfway mark for simple majority.
"Kumaraswamy moved the motion for trust vote. As per the procedure, voice vote was conducted first, followed by division of voters after opposition BJP leader B.S. Yeddyurappa pressed for division. I will vote only if there is a tie. To save the dignity of the chair, I will not vote now," the Speaker said in Kannada.
In the division of votes, 99 were for the motion and 105 against it.
Of the 20 legislators who were absent for the floor test, 15 were rebels of the Congress-JD(S) coalition, two Congress members who are in private hospitals in the city and in Mumbai for treatment, two Independents and one Bahujan Samaj Party (BSP) member.
Soon after the floor test, BSP supremo Mayawati expelled N. Mahesh, the party's MLA from Kollegal in Karnataka, for abstaining from voting.
The political crisis gripped the 14-month-old fledgling government in Karnataka after 13 Congress and 3 JD-S rebels resigned between July 1 and July 10 in protest against decisive leadership and lack of development across the southern state.
Senior Congress lawmaker and former minister R. Ramalinga Reddy, however, withdrew his resignation and voted in favour of the motion.
Though the BJP sought Kumaraswamy's resignation for losing majority in the Assembly after the rebels refused to withdraw their resignations and two Independents, who were ministers in his 34-member cabinet, withdrew their support on July 8, a defiant outgoing Chief Minister moved the confidence motion to prove majority in the hope the rebels will return to the coalition fold.
( With inputs from IANS )