Stephen Hester, the chief executive of Royal Bank of Scotland (RBS), is giving evidence to politicians, amid reports that he is in line to receive a bonus of £780,000.
The chairman of the bank, Sir Philip Hampton, will also later appear before the Parliamentary Commission on Banking Standards.
The session comes less than a week after the bank was fined £390m by regulators in the UK and US for its part in rigging the Libor inter-bank lending rate.
Around £300m of this penalty will be clawed back from the bonus pool at RBS, which is 82% owned by the taxpayer.
Despite this, Mr Hester will be paid a bonus worth £780,000 next month, according to media reports.
The pay-out is likely to anger critics of such schemes across the City, coming so soon after the Libor scandal rocked RBS.
The Sunday Times said the shares-based bonus was awarded in 2010 and deferred for three years.
The outgoing head of RBS' investment banking division, John Hourican, will also face MPs and peers later.
Mr Hourican, who was brought in to rescue the business after it was bailed out in 2008, forfeited around £4m in share options awarded to him based on past performance, but will leave the bank with 12 months’ pay worth £775,000.
In a memo to bank staff obtained by Sky News , he said he bore "some responsibility" for misconduct, despite having no involvement in or knowledge of efforts to rig Libor submissions by RBS staff.
The bank's former chairman of global banking and markets, Johnny Cameron, will also appear before the Commission.