Business Insider reports that Mick Mulvaney, President Trump's former chief of staff, told CNBC on Thursday that he resigned.
Mulvaney who was serving as special envoy to Northern Ireland, said "I can't do it. I can't stay."
His decision comes after pro-Trump mobs staged an attack on the Capitol, which postponed the certification of Joe Biden's election victory.
Mulvaney is the latest in a string of officials who have resigned since Wednesday's event.
He suggested that more resignations will come.
Mulvaney's decision to quit follows White House officials that include: Deputy Press Secretary Sarah Matthews, the First Lady's Chief of Staff Stephanie Grisham, and Deputy National Security Advisor Matthew Pottinger.
He also said that some colleagues plan to stay "because they're worried the president might put someone worse in."