Michael T. Flynn resigned as national security adviser on Monday night following the revelation that he had misled White House officials about conversations he had had with the Russian ambassador to the United States.

Here’s a timeline of his tenure.

Nov. 18

President-elect Donald J. Trump offered Mr. Flynn the post of national security adviser, elevating the retired general and intelligence officer who saw Islamist militancy as a global existential threat.

“I am pleased that Lt. Gen. Michael Flynn will be by my side as we work to defeat radical Islamic terrorism, navigate geopolitical challenges and keep Americans safe at home and abroad,” Mr. Trump said at the time.

Dec. 29

Former President Barack Obama ejected dozens of suspected Russian intelligence operatives from the United States and imposed sanctions on Russia after American intelligence officials concluded that the nation had ordered the hacking of the Democratic National Committee in an attempt to tip the election to Mr. Trump.