Green and Avro have announced they are leaving the energy market and will cease trading.
The announcement from Green came just one day after it was reported the firm had lined up insolvency advisers.
The supplier said it was "exiting the market due to the government failing to provide any support to smaller energy suppliers," Sky News reported.
The firm supplies around 250,000 customers and employs more than 180 people.
Avro Energy, which supplies 580,000 people, also announced it had gone bust on Wednesday afternoon and said energy regulator Ofgem.
A statement on Avro's website said: "Customers need not worry, their supplies are secure and domestic credit balances are protected."
It comes as the boss of Ofgem said that the country's current pace of soaring gas prices is something the watchdog has not seen before.
Chief executive Jonathan Brearley added that "well above" hundreds of thousands of customers could be affected by the hike.
Business and energy secretary Kwasi Kwarteng slammed energy companies calling for a lifting of the price cap so they could pass on soaring gas costs to consumers on Wednesday.
Suppliers went into business with their "eyes open," Kwarteng told MPs, after refusing to bail out failing suppliers.
The secretary said he was committed to keeping the price control, which caps household energy costs at £1,277 a month.
A handful of challenger energy companies have collapsed following price rises including People's Energy and Utility Point.
What's more, the UK's sixth-largest energy company, Bulb, looked to secure an emergency cash injection to avoid collapse, seeking advice from investment bank Lazard.
Some analysts have estimated that the number of energy companies in the UK could be reduced to three-quarters over the coming months, with as few as 10 left.
By City AM
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