Pressure was mounting on Nadhim Zahawi after it emerged he paid a tax penalty while chancellor.
Nadhim Zahawi has been sacked as Conservative Party chairman amid mounting pressure over his tax affairs.
The prime minister said an inquiry into Mr Zahawi’s financial affairs showed there was a “serious breach of the ministerial code”.
Rishi Sunak ordered the investigation after it emerged Mr Zahawi paid a penalty to HMRC while he was chancellor, over previously unpaid tax.
Mr Zahawi had said HRMC accepted it was a “careless and not deliberate” error.
In a letter to Mr Zahawi, Mr Sunak said the MP could be “extremely proud of your wide-ranging achievements in government over the last five years”.
He specifically cited Mr Zahawi’s work overseeing the Covid vaccine, saying it was “critical to ensuring our country came through this crisis and saved many lives”.
Mr Zahawi had come under increased scrutiny after he confirmed he had made a payment to settle a dispute with HM Revenue & Customs (HMRC).
The BBC understands the dispute was resolved between July and September last year, when he was chancellor and in charge of the tax system.
The total amount paid was in the region of about £5m, including a penalty, the BBC understands.
On Monday, Mr Sunak had asked his independent ethics adviser, Sir Laurie Magnus, to look into the disclosures about Mr Zahawi’s tax affairs, saying there were “questions that need answering”.