Sharp was formerly Sunak's boss at investment bank Goldman Sachs and is a donor to the ruling Conservatives party.
BBC chairman Richard Sharp has resigned from his position.
He announced his resignation on Friday, April 28 after an inquiry found he had breached rules for failing to declare his involvement in arranging a loan for then UK prime minister Boris Johnson.
Controversy surrounding the appointment of Sharp to head the BBC had heaped pressure on Johnson's successor Rishi Sunak.
A week ago, Sunak lost his deputy prime minister, Dominic Raab, who was forced out after another inquiry found him guilty of bullying civil servants.
Sharp was formerly Sunak's boss at investment bank Goldman Sachs and is a donor to the ruling Conservatives party.
The chairman of the British Broadcasting Corporation is appointed by the UK monarch on the advice of the government.
Sharp's appointment by Johnson was criticised at the time with allegations of favoritism. ..
Sharp "failed to disclose potential perceived conflicts of interest" to a committee of MPs who were vetting his appointment by Johnson in early 2021, the inquiry by a senior UK lawyer found.
"There is a risk of a perception that Mr Sharp was recommended for appointment because he assisted... the former prime minister in a private financial matter," lawyer Adam Heppinstall found.
In February, the same committee of MPs accused Sharp of "significant errors of judgement" for not disclosing his involvement in the loan.
While he was being considered for the BBC job, Sharp in late 2020 put Johnson in contact with a distant cousin of the prime minister who extended him a credit facility of £800,000 ($1 million).
Sharp on Friday denied he got the job as a quid pro quo for helping out Johnson, but announced his resignation hard on the heels of Heppinstall presenting his report to Sunak's government.
He acknowledged breaching conflict-of-interest rules for top UK officials, but said it was "inadvertent and not material" to his appointment to the BBC.
"Nevertheless, I have decided that it is right to prioritise the interests of the BBC," he said in a statement, confirming he would step down at the end of June to give time for a new chair to be found.
"I feel that this matter may well be a distraction from the Corporation's good work were I to remain in post until the end of my term."