Manasseh Sogavare has pointed to governance failures, missing mining revenues and "very narrow-gripped" leadership after abandoning the government of his former ally Jeremiah Manele.
The former Solomon Islands Prime Minister is also not ruling out a fifth stint in the top job should the government fall, as expected, on May 6.
Mr Sogavare, 70, headlined a surprise exodus of ministers and MPs from the coalition government on Monday.
On Tuesday in parliament, a new grouping including Opposition Leader Matthew Wale, Mr Sogavare, and ex-infrastructure minister Manasseh Maelanga claimed a majority, and will test that with a no-confidence motion in Mr Manele next Tuesday.
The episode is the latest example of unfixed loyalties in Solomon Islands politics, given just last year Mr Wale told the ABC Mr Sogavare was a "con man".
Fronting journalists in Honiara this week, Mr Sogavare said the political crisis would "not have reached this stage had the prime minister acted decisively and in the national interest".
"Critical signs of instability were ignored by the prime minister ... he had the assumption that things would iron themselves out. That's not how you deal with issues."
Speaking to the ABC, Victoria University of Wellington Professor John Fraenkel said this comment was "disingenuous".
"The cause of the instability in the governing coalition is him and the other 10 members of the governing coalition that resigned," he said.
While the new grouping claims to have a majority of 26 MPs in the 50-seat parliament, those numbers may change in the days before the no-confidence motion is heard in parliament.
It is also unclear who would be prime minister should Mr Manele fall, with Mr Wale - who lost a prime ministerial ballot last May - and Mr Sogavare both natural candidates.
Mr Sogavare said he had "never, never, never in my life fought to become prime minister" in the past, insisting it had been offered to him on the previous four occasions during times of crisis.
"We have come here as a new coalition, and the new coalition too will decide on who will be our candidate for prime minister," he said.
Mr Sogavare hinted at improper behaviour by the deputy prime minister and mines minister Bradley Tovosia, who also resigned on Monday.
Mr Tovosia's exit, announced by the prime minister's office, was interpreted as a move by Mr Manele to coax the rebels back into his tent.
"When it comes to how much minerals are going out, and how much money is coming in, there is nothing like that. No records," Mr Sogavare said.
"There are people that actually want to carry the minerals in planes out of the country (and) when this happens, the money did not come here. It's money that has gone outside of the country.
"These are probably issues that are subject of investigation at some point in time. So we will leave it there, as it is not appropriate to talk about it here."
Another MP to walk out, West Kwaio MP Claudius Tei'ifi, said he left due to lack of progress in an Australian-supported development of an international port and tuna processing plant at Bina Harbour.
"Our economy has hit rock bottom. We need leadership that puts national projects like Bina Harbour at the forefront of economic recovery," Mr Tei'ifi told In-depth Solomons.
Mr Wale and Mr Manele are also expected to hold media conferences this week in Honiara.
