WASHINGTON — Jack Smith, the special counsel who pursued two federal prosecutions of former President Donald Trump, plans to finish his work and resign along with other members of his team before Trump takes office in January, people familiar with his plans said.

Smith’s goal, they said, is to not leave any significant part of his work for others to complete and to get ahead of the president-elect’s promise to fire him.

Smith, who since taking office two years ago has operated under the principle that not even a powerful ex-president is above the law, now finds himself on the defensive as he rushes to wind down two complex investigations slowed by the courts and ultimately made moot by Trump’s electoral victory.

Smith’s office is still drawing up its plan for how to end the cases against Trump: conspiring to overturn the 2020 election and mishandling classified national security documents after leaving office and obstructing efforts to retrieve them. It is possible that unforeseen circumstances — such as judicial rulings or decisions by other government officials — could alter his timeline.

The election’s outcome spelled the end of the federal cases against Trump, since Justice Department policy has long held that a sitting president cannot be prosecuted for crimes. A Supreme Court ruling this summer expanded the scope of official presidential conduct that can’t be prosecuted even after leaving office.

Department regulations call for him to file a report summarizing his investigation and decisions — a document that may stand as the final accounting from a prosecutor who filed extensive charges against a former president but never got his cases to trial.

It is not clear how quickly he can finish this work, leaving uncertain whether it could be made public before the Biden administration leaves office.

But several officials speaking on condition of anonymity said he has no intention of lingering any longer than he has to, and has told prosecutors and FBI agents on his team who are not directly involved in that process that they can start planning their departures over the next few weeks, people close to the situation said.

Smith, a former war crimes prosecutor, is now a target of pro-Trump Republicans who portray him as the embodiment of a Democratic effort to use “lawfare,” the so-called weaponization of the Justice Department, to destroy Trump.