Dominic Raab has revealed that two formal complaints have been made about his behaviour during previous stints as a cabinet minister.
Prime Minister Rishi Sunak has agreed with a request by the deputy PM and justice secretary for an independent inquiry into the complaints.
Mr Raab has faced a series of newspaper allegations he bullied officials in previous roles, which he has denied.
He added he would “co-operate fully” with any inquiry into his conduct.
In a letter to Mr Sunak, Mr Raab said the complaints related to his time as justice secretary and foreign secretary under former Prime Minister Boris Johnson.
He added he had “never tolerated bullying” and had “always sought to reinforce and empower” civil servants.
Mr Raab’s letter came ahead of Prime Minister’s Questions, where he stood in for Mr Sunak – who is at the G20 summit in Indonesia.
Mr Raab told MPs he understood the complaints against him were made on Tuesday, and he was notified on Wednesday morning.
He added he was “confident that I have behaved professionally throughout”.
“I will thoroughly rebut and refute any of the claims that have been made,” he added.
Mr Sunak told reporters on Tuesday morning UK time he was unware of any formal complaints against his deputy PM.
In a letter replying to Mr Raab, Mr Sunak said: “I know that you will be keen to address the complaints made against you and agree that proceeding in this way is the right course of action.”
However, he gave no details of when an investigation would begin or who would conduct it.
Such a probe would normally fall within the remit of the PM’s adviser on ministerial conduct.
However, that position has been vacant since the previous occupant Lord Geidt quit in June after conceding Mr Johnson may have broken ministerial rules over Partygate.
Asked by Labour deputy leader Angela Rayner at PMQs when a replacement would be appointed, Mr Raab replied a recruitment process was under way and “taking place at pace”.
Mr Raab was sacked as justice secretary and deputy prime minister by former PM Liz Truss when she took power in September.
But the Esher and Walton MP was reappointed to both roles by Mr Sunak following his election as Conservative leader by the party’s MPs.
On Tuesday, the former top civil servant at the Foreign Office said colleagues were “scared” to go into Mr Raab’s office when he was foreign secretary.
Lord McDonald told Times Radio Mr Raab was “very curt with people” and “people felt demeaned.”
The peer said he “had several conversations” with Mr Raab about his behaviour, but was not aware of any formal complaints about it.
