Daniel Werfel, the commissioner of the Internal Revenue Service, told the agency’s employees that he would end his term early and step down on Monday as President-elect Donald J. Trump takes office.
Mr. Trump has said he plans to nominate Billy Long, a former Republican congressman, to the role. Past presidents have treated the tax collector’s leader as a nonpartisan job that continues between administrations of different parties. President Biden chose Mr. Werfel, a former career civil servant and management consultant, to attempt a renaissance of the I.R.S., which Democrats have infused with billions in new funding that Republicans are now eager to cancel.
In a message to employees, Mr. Werfel said he had decided to step down after he concluded that it was the best way to support the next administration. Douglas O’Donnell, a career civil servant at the I.R.S. who currently has the No. 2 job, will serve as the acting commissioner, Mr. Werfel said.
“While leaving a job you love is never easy, I take comfort in knowing that the civil servant leaders and employees at the I.R.S. are the exact right team to effectively steward this organization forward until a new I.R.S. commissioner is confirmed,” he wrote.
With more than 80,000 employees, the I.R.S. is a central part of the federal government, collecting nearly $5 trillion in tax revenue last fiscal year. With $60 billion in additional funding approved by Democrats, the agency has in recent years tried to beef up tax collection for wealthy Americans and update its antiquated technology systems.
The I.R.S. has long been a villain to Republicans, who attack it as a political tool for Democrats. Mr. Long, Mr. Trump’s pick to lead the agency, has scant tax experience beyond promoting a pandemic-era tax credit for small businesses that the I.R.S. has tried to shut down because of abuse. Republicans have already canceled $20 billion of the $80 billion Democrats originally envisioned for the I.R.S., and they have frozen $20 billion more.